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UNIT – 1: BASIC BIOLOGY
CHAPTER-
CELL CYCLE, CELL DIVISION AND STRUCTURE OF
CHROMOSOME
Topic-
Cell Cycle and Cell Division
Concepts covered: Cell cycle, Cell Division, Structure of chromosome and DNA, Homologous chromosomes and variations as a result of crossing over
Revision Notes
All living beings are made up of one or more units called cells.
The organisms made up of a single cell are called
unicellular organisms while the organisms that consist of many cells are known as multicellular organisms.
The study of cell is called cytology. The term cell was given by Robert Hooke for the first time when he observed cork cells under a primitive microscope assembled by him.
Cell Theory : The credit of formulation of cell theory
is given to a German Botanist M.J. Schleiden and a German Zoologist T. Schwann. Cell theory states that: (a) All living organisms are made up of cells. (b) Cells always arise from the pre-existing living cells with the help of division.
Growth is a continuous process which occurs
throughout the life of a cell.
Each and every cell in an organism possesses three
essential parts – cell membrane, cytoplasm and nucleus.
Cell cycle:
It is the sequence of events including growth and
division, that cell undergoes from the time of its formation up to its division into daughter cells.
Cell cycle comprises of two phases – Interphase and phase of division (mitosis or meiosis i.e., M Phase.)
G 1 , S, G 2 and M – phase collectively form the cell cycle.
Interphase:
It is a series of changes that takes place in a newly
formed cell and in its nucleus before it becomes capable of dividing again. Therefore, it is also called intermitosis.
Interphase of dividing cell has three stages - G 1 , S and
G2 -phase.
It is also known as biosynthetic phase in which cell duplicates its cell organelles & replicates its DNA. G 1 phase is characterised by the synthesis of RNA and non-histone proteins. Cell growth occurs and substances are produced which inhibit or stimulate the onset of next S – phase. S phase follows the G 1 - phase. It is characterised by the replication of DNA and the chromosomes are completely duplicated. G 2 - phase is the period in which centrioles, mitochondria, Golgi bodies and other cytoplasmic organelles are doubled. M or D phase: It is the phase when the cell enters the prophase stage of cell division. Phase of division- Mitosis Mitotic (M–phase) consists of karyokinesis (division of nucleus) and cytokinesis (division of cytoplasm). Mitosis results in the formation of identical cells. Daughter cells have same genetic constitution quantitatively and qualitatively as the original cell. Mitosis was first observed by Strasburger in plant cells and by Flemming in animal cells. In some cells like gamete mother cells or sporogenous cells mitosis is replaced by meiosis. Karyokinesis: Karyokinesis: It comprises of four phases – prophase, metaphase, anaphase and telophase. Prophase: It is the longest phase of division. Replicated chromosomes each with two sister chromatids condense and become visible. Nuclear membrane along with nucleolus disappear.
Metaphase: The chromosomes arrange themselves at the equator of the spindle to form the equatorial plate. Each chromosome is attached to the spindle fibres by its centromere.
Anaphase: The centromere splits and the newly- copied chromosomes (daughter chromatids) are moved to opposite poles of the cell.
Telophase: It is the phase in which nuclear membrane is reformed around each group of chromatids, now called chromosomes at each pole. Two nuclei are thus formed.
Karyokinesis is followed by cytokinesis in which cytoplasm of the cell divides in two parts. Importance of Mitosis: It brings about the reproduction in unicellular organisms.
It is necessary for growth, maintenance and repair in multicellular organisms.
Differences between Animal and Plant cell Mitosis :
Mitosis in Animal cell Mitosis in Plant cell
- Asters are formed. 1. Asters are not formed.
- Cytokinesis occurs by furrowing of cytoplasm. 2. Cytokinesis occurs by cell plate formation.
- Occurs in most tissues throughout the body. 3. Occurs mainly at the growing tips and sides.
Meiosis:
Meiosis is the cell division which occurs in sex cells and results in the formation of four daughter cells. The daughter cells are quantitatively and qualitatively different from mother cells.
The whole process consists of two successive coordinated divisions called meiosis – I and meiosis – II.
During meiosis – I, the number of chromosomes is reduced to half while in meiosis – II, division is of simple mitotic type. Meiosis maintains the same chromosome number through successive generation of species as in meiosis the number of chromosomes in the sex cells are halved and when these sex cells fuse during fertilisation, original chromosome number is restored. It helps to produce new recombination of characters as a result of crossing over (exchange of genetic material between two homologous chromosomes). Major differences between Mitosis and Meiosis are:
Mitosis Meiosis (a) Mitosis takes place in the somatic cells.
It occurs either in the reproductive cells or at the time of development of zygote. (b) It is a single division which produces two cells.
It is a double division. It gives rise to four cells.
(c) The number of chromosomes remains the same after mitosis.
The number of chromosomes get reduced to half after meiosis.
(d) No crossing over takes place.
Crossing over takes place in prophase - I.
Regulation of cell cycle The cell cycle is controlled by checkpoints to ensure that a previous phase is fully completed before advancing to the next phase. (a) Feedback from the cell determines whether the cycle switches to the next stage. (b) Three principal checkpoints i.e. G 1 , G 2 and M checkpoints: Control the cycle in eukaryotes.
Mnemonics
Concept: Cell cycle stages Concept: Mitotic stages Mnemonic: G et S et G o! M ake a Call Mnemonic: I P refer M ilk A nd T ea – C offee Interpretation : Interpretation : G : G 1 Phase G : G 2 Phase I : Interphase A : Anaphase
S : S Phase M : M Phase P : Prophase T : Telophase C : Cytokinesis M : Metaphase C : Cytokinesis
Key Terms
Crossing over: Exchange of respective chromatid segments in a homologous pair. Spindle fibres: The fibres which are present between the poles of the cell during cell division. Intermitosis: A process comprising of a series of changes that takes place in a newly formed cell and
in its nucleus before it becomes capable of dividing again. Biosynthetic Phase: Interphase is also known as biosynthetic phase cause it involves duplication of cell organelles and replication of DNA.
CHAPTER-
GENETICS
Topic-
Genetics and Related Terms
Concepts covered: Terms related to genetics likeMonohybrid, Dihybrid, phenotype, genotype, punnett square etc.
Revision Notes
Genetics The term genetics was proposed by William Bateson.
Genetics is the branch of biology that deals with the study of inheritance and variation of characters from parent to offspring.
The transmission of characters from parent to offspring is called heredity or inheritance. Like wise, no two individuals of a species are alike, such differences are called variations.
Terms Related to Genetics
Monohybrid Cross is the inheritance of one pair of contrasting characters. For example, a cross between a tall and a dwarf plant (short). The phenotypic ratio in F 2 -generation of monohybrid cross is 3:1. Dihybrid Cross is inheritance of two pairs of contrasting characters. For example, the inheritance of yellow and round seed character with the green and wrinkled character is a dihybrid cross. The phenotypic ratio in F 2 -generation of dihybrid cross is 9:3:3:1.
Phenotypic Ratio: 3 : 1 Tall - 3 Dwarf - 1
Gene: Mendel presumed that a character is determined by a pair of factors present in each cell of an individual. These are known as genes in modern genetics.
Allele or allelomorph : They are various forms of a gene or Mendelian factor which occur on the same locus on homologous chromosomes and control the same character. Alleles or allelomorphs control different expressions or traits of the same character (e.g., tallness and dwarfness in Pea).
Heterozygous: An individual having two contrasting Mendelian factors or genes for a character. Heterozy- gote or heterozygous individual is also called hybrid, e.g., Tt.
Homozygous: An individual having identical Men- delian factors or genes for a character (TT or tt). Ho- mozygous or homozygotic individual is always pure for the trait.
Punnett square: It is a graphical representation used for the calculation of probability of all possible genotypes of offspring in a genetic cross.
Mutation: A mutation is a change in the DNA sequence of an organism. Mutations can result from errors in DNA replication during cell division, exposure to mutagens or a viral infection.
Dominant Factor: An allele or Mendelian factor which expresses itself in the hybrid (heterozygote) as well as in the homozygous state. It is denoted by capital letter (T for tallness).
Recessive Factor: An allele or Mendelian factor which is unable to express itself in the hybrid or in the presence of alternate (dominant ) allele. It is denoted by small letter (t for dwarfness). The recessive factor expresses itself only in the homozygous state (e.g., tt ). Variation: The differences among the members of same species and offspring of the same parents are referred to as variation. Genotype: It is the gene complement or genetic constitution of an individual with regard to one or more characters irrespective of whether the genes are expressed or not. For example, the genotype of hybrid tall pea plant is Tt, pure tall TT and dwarf tt. Phenotype: The observable, morphological or physiological expression of an individual with regard to one or more characters is called phenotype. For recessive gene, the phenotype is similar to genotype. For dominant genes, the phenotypic expression can be due to its homozygous genotype or heterozygous genotype. For example, phenotypic tall pea plant can be genotypically TT or Tt.
Key Terms
Character: It is well defined morphological or phys- iological feature of an organism. e.g., stem height. Cross: Mating between two individuals which leads to the fusion of gametes are called cross.
Topic-2 Mendel’s Laws of Inheritance
Revision Notes
Introduction:
G. J. Mendel ( 1822-1884 ), the father of genetics, was an Austrian monk. He was the 1st^ scientist who made a systematic study of patterns of inheritance of characters from parents to progeny. He carried out breeding experiments on garden pea plants ( Pisum sativum ) and formulated basic laws of heredity.
Mendel crossed a pure tall garden pea plant and a pure dwarf pea plant, the resulting offspring were called F 1 generation.
Selection of Pea Plant Why Mendel selected pea plant for his experiments?
(i) Garden pea has distinct, easily detectable contrasting traits.
(ii) The plant reproduces well and grows to maturity in a single season.
(iii) The pea plant is self pollinating in nature because pea flower is bisexual. (iv) Self pollination could be prevented by removing the male reproductive parts of the flower. (v) Cross-pollination could be done artificially. Mendel’s Laws of Inheritance Law of Paired Factor: A character is represented in an individual ( diploid ) by at least two factors. The two factors lies on the two homologous chromosomes at the same locus. Law of Dominance: In a hybrid, where both the contrasting alleles or unit factors are present, only one unit factor /allele called dominant is able to express itself while the other factor/allele called recessive remains suppressed. In a cross between pure breeding tall plant (TT) pea plant and dwarf (tt) pea plant, the F 1 generation is tall though it has received both the factors (T and t).
Phenotypic Ratio – 9 : 3 : 3 : 1 Yellow, Round – 9 Yellow, Wrinkled – 3 Green, Round – 3
Green, Wrinkled– 1 This ratio is called Mendel’s dihybrid phenotypic ratio.
Mnemonics
Concept : Mendel’s Laws of Inheritance Mnemonics : D raw for S chool I nstitute Interpretation : Law of Dominance, Law of Segregation, Law of Independent Assortment
Key Terms
Progeny: The offspring of living organisms such as plants and animals.
Hybrid: The heterozygous organism produced after crossing two genetically different individuals is called a hybrid.
Topic-3 Sex Determination in Human Beings
Revision Notes
Human Chromosomes
In humans, 23 pair of chromosomes are present. These are classified into two main types such as – Autosomes and sex chromosomes. Autosomes are 22 pairs of chromosomes. Autosomes are chromosomes that contain genes for anything that are not related to sex determination. Sex chromosome is a pair of chromosome which determine the sex of a person. These XX-XY chromo- somes are called hetero-chromosomes or allosomes. In human beings, male gamete ( sperm ) contains either X or Y chromosome, while female gamete ( egg ) contains only X-chromosome. The sex of child depends upon the kind of sperm that fertilises the egg during fertilisation. In case, the sperm carrying (X) chromosome fertilises the egg (X), then the resulting child will be female (XX) and if the sperm carrying (Y) chromosome fertilises the egg (X), then the resulting child will be male (XY). This can be shown by the following cross:
Key Terms
Autosomes: Autosomes are chromosomes different from the sex chromosomes in a eukaryotic cell. Allosomes: A Pair if chromosomes that determine gender of a person are called allosomes.
Topic-4 Sex Linked Inheritance of Diseases
Revision Notes
Introduction
Sex linked inheritance was first discovered by T.H.
Morgan (1910) in Drosophila.
In man, two sex linked disorders are haemophilia
and colour blindness.
In haemophilia, blood clotting mechanism is absent. The person with colour blindness cannot distinguish colours. Haemophilia and colour blindness are caused by recessive genes present on X chromosome.
The above two disorders are common in males
than females, because the gene is located on the X chromosome. As there are two X chromosomes in females out of which only one gets affected usually, so, the disease is not expressed. On the other hand,
males have only one X chromosome, so the disease is expressed in males. Inheritance of Diseases When a normal man marries a colour blind female., expected ratio of their children may be shown as:
Result – All male children are colour blind and all female children are carrier.
Inheritance of X-liked genes as in colour blindness and haemophilia is called criss-cross inheritance.
This is because the son (male) may get it from the otherwise normal but carrier mother and a colour blind father may pass it on to the daughter making her colour-blind if the mother is carrier.
Mnemonics
Concept : Genetic Disorders Mnemonics : N ever C ome H ome A lone Interpretation : N ight Blindness, C olour blindness, H aemophilia, A lbinism
UNIT – 2: PLANT PHYSIOLOGY
CHAPTER-
ABSORPTION BY ROOTS AND TRANSPIRATION
Topic-
Processes of Water and Mineral Absorption
Concepts covered: Absorption by roots, imbibition, diffusion and osmosis; osmotic pressure, root pressure, plasmolysis and deplasmolysis, concept of transpiration and Ganong's potometer, Guttation and bleeding.
Revision Notes
Introduction
Plant physiology is the branch of Botany which deals with the study of metabolic activities or life processes of plants. Stephen Hales is considered as Father of plant physiology. Father of plant physiology in India, is Sir. J.C. Bose.
Water forms 66 % to 90 % of the total body weight of living beings. At least 75% of the mass of a plant is water.
Imbibition
Imbibition is the absorption of water by solid particles of an absorbent substance without forming a solution. e.g., swelling of seeds.
Imbibition is the phenomenon in which living or dead cells of plants in their dry or semi dry state absorb water by surface tension. It is the passive absorption of water by substances such as cellulose and starch. Imbibition results in an increase in volume, liberation of heat and development of pressure called imbibition pressure.
Diffusion Diffusion is the movement of molecules of a substance (gas, liquid or solid) from the region of higher concentration to the region of lower concentration.
Topic-
Absorption, Characteristics of Root and
Ascent of Sap
Concepts covered: Mechanism of absorption , active and passive absorption, role of root hairs in absorption,ascent of sap, root pressure and cohesive force theory.
Revision Notes
Absorption of Water
Absorption of water and minerals by plants mainly occur through roots. The maximum absorption takes place through root hairs located in the root hair zone lying just behind the root cap.
There are two distinct mechanisms of water absorption by plants – active absorption and passive absorption. These two mechanisms operate independent of each other.
Active absorption
Active absorption of the water involves the expenditure of metabolic energy (ATP) released through respiration.
In this process the root cells play active role in the absorption of water.
Passive absorption
Ions are absorbed from the region of their higher concentration to their lower concentration along the concentration gradient without requiring any metabolic energy and it takes place by: a. Mass flow b. Diffusion and c. Ion exchange Passive absorption is mainly due to transpiration, where the root cells do not play any active role, but they remain passive. This process does not require the expenditure of metabolic energy. Passive absorption of water accounts for about 98% of total water uptake by a plant. Root Hairs
Root hairs play very important role in the absorption of water.
These are tubular outgrowths of epiblema cells present just above the zone of elongation.
Because of their narrow nature they can pass easily into soil interspaces where capillary water is available for absorption.
Cell sap of central vacuole exerts an osmotic pressure for absorption of water.
Ascent of Sap
Upward transport of water to aerial parts along with the dissolved mineral salts from roots to the aerial parts against the downward pull of gravity is called ascent of sap. Ascent of sap takes place through xylem. Several theories has been put forward to explain the mechanism of ascent of sap. These are Vital force theory, Root pressure theory, Capillary force theory and Cohesive force theory. Today most of the workers believe in the Cohesive force theory (Cohesion tension theory). Root pressure: The pressure developed in the roots due to inflow of water, which helps in pushing the plant sap upwards is called root pressure. Cohesive force theory Cohesive force is the force created due to mutual attraction between water molecules. Due to transpiration, large quantity of water is lost. Water forms a continuous column in the xylem of the leaves to the xylem of the root. Due to cohesion, the water column does not break. Cohesion of water and transpiration pull (tension) theory was given by Dixon and Jolly (1894). It was further improved by Dixon in 1914. According to this theory, a tension (transpiration pull) is created in water in the xylem elements of leaves due to constant transpiration. This pulls water to the top of the tree. The continuity of water column in the xylem is maintained due to cohesive and adhesive force of water. This theory is widely accepted.
Mnemonics
Concept : Pathway of water absorption in plants Mnemonics : RECEP to R X (receptor X) Interpretation : Root hair, Epidermis, Cortex, Endodermis, Pericycle, to Root Xylem.
Key Terms
Metabolic Energy: The energy required for cellular processes, including growth, maintenance, and reproduction, derived from metabolic pathways that convert nutrients into usable forms, such as ATP, in living organisms. Epiblema Cells: The outermost layer of young plant roots that functions in the absorption of water and
nutrients from the soil, protecting the root tip and participating in root-hair formation. Cohesive and Adhesive Forces: Cohesive forces are the intermolecular attractions between similar mole- cules, while adhesive forces are attractions between different molecules. Both contribute to phenomena like capillary action and surface tension in liquids.
Topic-3 Transpiration
Revision Notes
The loss of water in the form of water vapours from the aerial (living) parts of the plant is called transpira- tion.
CoCl 2 paper method is used to compare the rates of transpiration. Moisture coming out from stomata turn blue CoCl 2 paper pink.
Types of Transpiration
There are three types of transpiration: stomatal, cuticular and lenticular
(a) Stomatal transpiration: occurs through stomata.
(b) Cuticular transpiration: occurs through cuticle of leaves & green herbaceous stems.
(c) Lenticular transpiration: occurs through lenticels present on woody stems.
Ganong’s Potometer method of measuring the transpiration is based on the assumption that the rate of absorption of water is approximately equal to the rate of transpiration.
Transpiration is more rapid during day than night because stomata closes during night.
Mechanism of Transpiration
Mechanism of stomatal transpiration can be briefly described in the following points –
(i) The water from saturated cells of spongy parenchyma evaporates and comes into intercellular spaces. (ii) The water vapours from the intercellular spaces diffuse into outer environment through stomata. (iii) Parenchymatous cells draw water from adjoining cells. Thus, it continues till they draw water from tracheary elements. Adaptations in Plants to Reduce Transpiration There are various adaptations in plants to reduce transpiration like: (i) Leaves reduced to spines to reduce the surface area for transpiration. (ii) Waxy leaf cuticle, which is impermeable to water and stops evaporation. (iii) Reduced number of stomata which reduces the transpiration rate. Many arid climate plants have specialised form of photosynthesis, which is called CAM photosynthesis. In these plants, the stomata remain shut during the day to reduce evaporation but open at night to collect carbon dioxide. Many chemicals (anti-transpirants) have been found to reduce the rate of transpiration without affecting CO 2 uptake, e.g. Phenyl mercuric acetate (a fungicide), and abscisic acid. Silicon emulsion & low viscosity waxes cover stomata as a film, allow CO 2 & O 2 exchange but resist diffusion of water. Guttation and Bleeding Guttation is the loss of water in the form of liquid drops. It usually occurs due to root pressure. Bleeding is the exudation of sap or watery solution from the cut or injured parts of the plants.
Mnemonics
Concept : Environmental Factors affecting Transpiration Mnemonics : Let’s Work Together in HomeWork Interpretation : Light, Wind, Temperature, Humidity and Water availability.
Key Terms
Parenchyma: A type of simple plant tissue consisting of living cells with thin cell walls, involved in various physiological functions such as photosynthesis, storage, and secretion in plant organs. Tracheary Elements: Specialized plant cells, includ- ing tracheids and vessel elements, that form the
water-conducting system (xylem) in vascular plants, facilitating the movement of water and minerals. Emulsion: A colloidal dispersion of one liquid in another, typically immiscible, where small droplets of one liquid are evenly distributed in another, often stabilized by emulsifying agents.
Mechanism of photosynthesis
Photosynthesis consists of two stages – the light phase and the dark phase. Light Phase: In the light phase, light is absorbed and used by chlorophyll. This, is called the photochemical reaction or Hill’s reaction. It can be described in two steps – Photolysis and formation of assimilatory powers. Photolysis is the process of splitting of water in the presence of light. Water splits into H+^ and OH–^ ions. H+^ ions go to NADP+^ while OH–^ ions form water, oxygen and electron in the presence of Z complex enzymes, Mn+² and Cl–^ ions. 4 H 2 O 4 H+^ + 4OH–
Mn+², Cl–, Z complex 4OH–^ 2H 2 O + O 2 ↑ + 4e– Assimilatory powers [ATP and NADPH] are formed in non-cyclic photophosphorylation. These assimilatory powers are used in dark reaction. The assimilatory powers are for fixation of CO 2 into glucose. Photophosphorylation is the process in which ADP (Adenosine Diphosphate) is converted into ATP (Adenosine Triphosphate) by the addition of one phosphate (Pi) group, i.e., inorganic phosphate, utilising the energy from photons. ADP + Pi ATP
Dark Phase: Dark reaction (biosynthetic phase) or Calvin cycle or Blackman’s reaction involves the fixation and reduction of CO 2 resulting in the formation of carbohydrates. The dark phase occurs in the stroma of the chloroplast where all the enzymes necessary for CO 2 fixation and synthesis of sugar and starch are located. RuBP (Ribulose bisphosphate) acts as a primary acceptor of atmospheric CO 2 in the beginning of this phase and by the utilisation of ATP and NADPH (products of light reaction), glucose is synthesised and RuBP is regenerated. The overall reaction of this phase is: 6 RuBP + 6 CO 2 + 18 ATP + 12e–^ 6 RuBP + C 6 H 12 O 6 + 18 ADP + 18 Pi + 12 NADP + 6H 2 O The hydrogen ions combine with CO 2 to form glucose. Glucose produced during photosynthesis is soluble in water and consists of small molecules. As soon as glucose is produced, it is converted into starch by the process of polymerisation. The starch is insoluble in water. It is stored in the parts of the plant for later use.
RuBPRuBP
NADPH( From Light Reaction)
NADP
ATP ADP+Pi
Calvin-Benson Cycle (light independent reaction)
Glucose (C H 6 12 O ) 6 Starch
CO 2 (From atmosphere)
Adaptation of a leaf for photosynthesis
Large surface area to maximise light harvesting. Thinness of leaves to reduce distance for CO 2 to diffuse through the leaf and to ensure that light penetrates into the middle of the leaf. Arrangement of chloroplast on the upper surface of leaves so as to receive maximum amount of light. Presence of more stomata to allow rapid exchange of gases (CO 2 and O 2 ).
Loosely packed spongy mesophyll cells help to trap carbon dioxide gas, allowing some photosynthesis even when the stomata are closed.
Mnemonics
Concept : Photosynthesis Reaction Mnemonics : C ows E at W et G rass O utside Interpretation : Carbon dioxide+Energy+Water → Glucose+Oxygen
Key Terms
Anabolic: Anabolic processes involve the synthesis of complex molecules from simpler ones in living organisms, requiring energy input. Examples include protein synthesis and the building of cellular structures. Exosmosis: Exosmosis is the outward movement of water across a membrane from an area of higher to lower concentration, driven by osmotic pressure, balancing water levels in cells.
Polymerization: Polymerization is a chemical pro- cess where monomers combine to form polymers through covalent bonds. This results in the creation of larger, more complex molecules, such as proteins and DNA. Chloroplast: Chloroplasts are organelles in plant cells responsible for photosynthesis. They contain chlorophyll, capturing light energy to convert carbon dioxide and water into glucose, releasing oxygen as a by product.
Topic-
Different Experiments and Factors Affecting
Photosynthesis
Concepts covered: test for photosynthesis, carbon dioxide, light and chlorophyll are necessary for photosynthesis and external and internal factors affecting photosynthesis
Revision Notes
Different Experiments on Photosynthesis
Test for photosynthesis : Leaf is killed in boiling water ( 5-10 minutes ), dried, decolourised in warm spirit, moistened and dipped in iodine solution. Blue black colour indicates starch.
CO 2 is necessary for photosynthesis/Moll’s half leaf experiment : One half of destarched leaf is inserted in air tight wide mouthed bottle having small quantity of KOH ( for absorption of CO 2 ) and illuminated. Starch test after one hour indicates absence of CO 2 in inserted half and presence in outer half (where CO 2 is available ).
Light is necessary for photosynthesis : Intact leaf of a destarched plant is fitted in Ganong’s light screen with a designed cut in its lid. The same is exposed to light for some time and then tested for starch. Only the design through which light falls on the leaf be- comes blue coloured.
Chlorophyll is essential for photosynthesis: Illu- minated variegated leaf of Coleus plant is tested for starch. Only those areas turn blue which had chloro- phyll.
Factors affecting Photosynthesis
External Factors
Light: Photosynthesis is successfully accomplished in the visible light (380 – 760 nm wave-length) of the spectrum. Rate of photosynthesis is maximum in red light, average in blue light and minimum in green light. A moderate light intensity is favourable for high rate of photosynthesis.
Carbon dioxide: 0.03 % CO 2 is present in atmosphere. Increase in CO 2 concentration upto 0.9% increases the rate of photosynthesis but concentration above 0.9% is harmful and decreases the rate of photosynthesis. Temperature: Generally, the photosynthesis increas- es with an increase in temperature in the range of 10-35°C. Beyond the 35°C, the rate of photosynthesis decreases. Water: About 1% total water absorbed is used in photosynthesis. Water deficiency reduces the rate of photosynthesis.
Internal Factors Chlorophyll : It is essential for photosynthesis to occur. The rate of photosynthesis per unit of chlorophyll decreases with the age of leaf. Accumulation of end product of photosynthesis : The rate of photosynthesis falls with the accumulation of food synthesised by photosynthesis. Anatomy of leaf: Photosynthesis rate is greatly influenced by the internal structure of the leaf, thickness of the cuticle and epidermis, number, structure and distribution of stomata.
Mnemonics
Concept: Factors Affecting Photosynthesis Mnemonics: L et’s T ake W hite C andy! Interpretation: Light, Temperature, Water, Carbon dioxide.
Key Terms
Variegated Leaf: A variegated leaf exhibits varia- tions in color or pigmentation, often due to uneven distribution of chlorophyll. This can result in dis- tinct patterns of colored and non-colored areas on the leaf. Light Intensity: Light intensity refers to the amount of light energy per unit area. It affects photosynthesis, growth, and development of plants, with variations influencing plant responses and adaptations.
Cuticle: The cuticle is a waxy, protective layer covering the outer surface of plant leaves and stems. It helps reduce water loss by evaporation and provides a barrier against pathogens. Stomata: Stomata are tiny pores on the surface of plant leaves and stems, facilitating gas exchange (oxygen and carbon dioxide) and water vapor release. They are crucial for photosynthesis and transpiration.
exposed to ethylene gas. These responses are typically observed in seedlings and involve:
Elongation Inhibition: The first phase involves the in- hibition of stem elongation. Ethylene suppresses the growth of the stem, leading to a compact and stunted appearance.
Radial Swelling: The second phase consists of radial swelling, causing the stem to thicken. This is a compensatory mechanism to counteract the inhibition of elongation, resulting in a more robust structure.
Horizontal Growth (Apical Hook Formation): In the final phase, ethylene induces horizontal growth and the formation of an apical hook. The seedling bends in a horizontal direction, which can be observed as a hook-like structure, aiding the seedling in penetrating the soil.
The triple response is a protective adaptation of seedlings to environmental stress, allowing them
to navigate obstacles and optimise their chances of successful establishment. Physiological effects of Ethylene: (a) Induces ripening of fruits. (b) Inhibits elongation but induces isodiametric enlarge- ments of cells. (c) Stimulates seed germination in some species. (d) Promotes leaf abscission. (e) Induces root hair formation. (f) Controls auxin level in tissues.
Mnemonics
Concept : Plant Hormones Mnemonics : A CAGE Interpretation : Auxin, Cytokinins, Abscisic Acid, Gibberellins, Ethylene
Key Terms
Growth Promoters: Substances that stimulate plant growth by enhancing cell division and elongation, often plant hormones like auxins and gibberellins, promoting overall development and productivity. Growth Inhibitors: Compounds, often hormones like abscisic acid, that regulate plant growth by suppressing cell division and elongation, controlling processes such as dormancy and stress responses. Cambium: A meristematic tissue in plant stems and roots responsible for secondary growth, producing xylem and phloem cells, contributing to the thickening and strengthening of the plant. Tissue Culture: In vitro cultivation of plant cells, tissues, or organs under controlled conditions, allowing the production of genetically identical
plants and the study of various physiological and developmental processes. Dormancy: A physiological state where a plant undergoes reduced metabolic activity and growth, often in response to adverse conditions, until environmental cues trigger renewed growth and development. Interfascicular Cambium: A type of lateral meristem located between vascular bundles in dicot stems, contributing to secondary growth by producing new vascular tissue, enhancing structural support and transport efficiency. Senescence of Leaves: The natural aging process of leaves involving programmed cell death, nutrient remobilisation, and chlorophyll degradation, leading to leaf yellowing and eventual shedding from the plant.
Topic-
Tropic Movements
Concepts covered: Phototropism, geotropism, hydrotropism, thigmotropism and chemotropism
Revision Notes
Plant Movements Plant movements in response to stimuli from some direction like light, gravity, chemicals and water are called tropic movements. It may be favourable towards the stimulus when it is positive or away from the stimulus when it is negative.
Phototropism : This is the growth movement of curvature induced by external stimulus of light. The shoots bend towards light (positively phototropic) while roots move away from light (negatively phototropic).
Geotropism : Growth movements induced by the stimulus of gravity are known as geotropism.
Shoot system grows away from gravity and is negatively geotropic. The roots grow towards gravity and are positively geotropic.
Some organs do not respond to geotropic stimulus and are called ageotropic, e.g., coralloid roots of Cy- cas. Hydrotropism : Growth movement in response to external stimulus of water is called as hydrotropism. Roots bend towards the source of water and are called positively hydrotropic. Thigmotropism : These are the movements due to contact with a foreign body. Tendrils, twinners, petiole of Clematis show thigmotropic movements. Poor growth on the side of contact and more growth on the other side results in coiling. Chemotropism : The curvature takes place due to some chemical stimulus. Fungal hyphae, pollen tube exhibit positive chemotropic movements due to some chemicals.
Key Terms
Movement of Curvature: The adaptive bending or turning of plant organs, such as stems, roots, or leaves, in response to external stimuli like light (phototropism), gravity (gravitropism), or touch (thigmotropism), optimising growth and development. Coralloid Roots of Cycas: Specialised roots found in certain cycads, like Cycas species. These roots form a symbiotic association with nitrogen-fixing cyanobacteria, contributing to the plant's nitrogen nutrition. The coralloid roots have a unique, swollen appearance due to the presence of the cyanobacterial colonies.
Mnemonics
Concept : Tropic Movements in plants Mnemonics : H ow T o P lay C ricket G ame? Interpretation : Hydrotropism, Thigmotropism, Phototropism, Chemotropism, Geotropism.
UNIT – 3: HUMAN ANATOMY AND PHYSIOLOGY
CHAPTER-
CIRCULATORY SYSTEM
Topic-
Body Fluids
Concepts covered: Blood and Tissue Fluid, Blood coagulation, Blood Group and Rh Factor, Struc- ture of Heart and its Functioning; Blood Vessels and Blood pressure; Double Circulation; Hepatic Portal System.
Revision Notes
Introduction
Circulatory system is one of the most important system of the body because it ensures the exchange of substances between cells of the body and external environment and transports them from one part to another.
Body fluids are the medium of transport in the body. These fluids have the ability to pick up substances and distribute them to various parts of the body.
Blood
Plasma
Blood platelets
RBCs (erythrocytes)
WBCs (leucocytes)
Smear of human blood
Lymph is the fluid along with some WBCs in intercellular spaces. Lymph acts as a middle man between blood and cells of tissues.
Mnemonics
Concept : Composition of blood Mnemonics : R ead, W rite and P lay Interpretation : RBCs, WBCs and Platelets
Key Terms
Connective Tissue: Connective tissue provides support and structure to the body, consisting of cells and an extracellular matrix with fibers and ground
substance. It is categorized into types like loose connective tissue, dense connective tissue, cartilage, bone, blood, and lymphoid tissue.
Plasmalemma: The plasmalemma, or cell membrane, is a phospholipid bilayer that surrounds a cell, defining its boundaries. It regulates the passage of substances and maintains the cell's structural integrity. Megakaryocyte: A megakaryocyte is a large bone marrow cell responsible for producing platelets,
which are crucial for blood clotting. Megakaryocytes undergo fragmentation to release platelets into the bloodstream.
Pathogen: A pathogen is a microorganism, such as a bacterium, virus, fungus, or parasite, that can cause disease in its host. Pathogens invade the host's tissues and can lead to infections.
Topic-
Blood Clotting, Blood Groups and Blood
Transfusion
Revision Notes
Blood Clotting
Blood clotting is the natural device to check bleeding.
Normal blood clotting time is 4-10 minutes.
Blood platelets accumulate at the site of injured tissue cells, which release thromboplastin or factor ‘X’.
Then thromboplastin with the help of Ca2+^ converts inactive prothrombin to active thrombin.
Thrombin acts as enzyme (Prothrombinase) along with Ca++. It reacts with soluble fibrinogen and converts it into soluble form or fibrin, a solid substance that forms threads and finally forms a clot.
Blood Group
Landsteiner (1900) discovered four blood groups in human, for which he was awarded Nobel prize.
The main blood groups are A, B, AB and O.
This grouping is mainly based on the type of antigen and antibodies present on the surface of red blood
corpuscles (RBC). The representation of different antigens and antibodies are depicted in the table given below:
S. No Blood groups Antigen Antibodies 1 A A B 2 B B A 3 AB A and B None 4 O None Both A and B
Blood of group A may be transfused to persons with blood group A and AB. Blood of group B may be transfused to persons with blood group B and AB.
Blood of AB group may be transfused to persons with blood group AB only. Blood of O group may be transfused to persons with blood group A, B, AB and O. O blood group can donate blood to all and hence is termed as universal donor. AB blood group persons can receive blood from all persons and hence are universal recipients.
Rh Factor
Landsteiner (1940) discovered a protein in the RBC of Rhesus monkey. Later, it was discovered in some human beings also. This protein was named as Rh factor /Rh antigen.
Persons having Rh antigen are described as Rh+ and those without this are described as Rh–. 93% of Indian people are Rh+^ and 7% are Rh–.
If Rh+^ blood is transfused to Rh–^ person, agglutination takes place. First transfusion is not serious, repeated transfusion with brief gap can cause death of the recipient.
Incompatibility during Pregnancy: A serious
problem arises for an Rh–ve mother. The Rh+ve blood of the foetus will stimulate the formation of anti Rh factors or antibodies in the mother’s blood. During the first pregnancy, , there is a possibility of exposure of the maternal blood to small amounts of the Rh+ve blood from the foetus. This induces the formation of Rh antibodies in maternal blood. In case of her subsequent pregnancies, the Rh antibodies from the mother leak into the blood of the foetus (Rh+ve) and destroy the foetal RBCs. This is fatal to the foetus or cause severe anaemia and jaundice to the baby. This condition is called Erythroblastosis fetalis.
Topic-3 Human Circulatory System
Revision Notes
Circulatory System
Circulatory system in human beings comprises a heart and blood vessels, i.e., arteries, veins and capillaries. In different organisms, circulatory system is of two types – open and closed circulatory system.
In open circulatory system, blood is pumped from the heart through blood vessels but then it leaves the blood vessels and enters into body cavity, e.g., arthropods, molluscs etc.
In closed circulatory system the flow of blood occurs inside the blood vessels and contains a respiratory pigment haemoglobin, e.g., human, birds etc.
Human Heart
Heart is the main pumping organ located in the thoracic cavity in human beings.
� It is enclosed in a double layered pericardium.
� The two layers of pericardi- um are separated by a narrow pericardial cavity which is filled with pericardial fluid.
� This fluid protects the heart from external shocks.
� In human beings, the heart is four-chambered.
Auricles - There are two auricles in the mammalian heart (left and right). They are separated from each other by inter auricular septum.
(a) Right auricle receives venous blood from different parts of the body (except lungs) through three major veins. These are two precaval veins and one post caval vein.
(b) Left auricle receives oxygenated blood from lungs. It is collected by pair of pulmonary veins.
Ventricles – There are two thick walled muscular ventricles (left and right) in mammalian heart.
� Left ventricle is wider than right one. � Auricles and ventricles are separated by an auriculo ventricular septum. � The two ventricles are separated from each other by an inter ventricular septum. � Right auricle opens into right ventricle through right auriculo ventricular aperture. It is guarded by a tricuspid valve. It allows the blood to flow into right ventricle only. � Left auricle opens into left ventricle through left auriculo ventricular aperture. It is guarded by bicuspid valve or mitral valve. It allows the blood to flow into left ventricle only. � From the right ventricle arises the pulmonary aorta which goes to lungs and carries deoxygenated blood. The opening of pulmonary aorta is guarded by three semilunar valves. � From the left ventricle, left systemic aorta arises and supplies oxygenated blood to all parts of the body. The opening between left ventricle and systemic aorta is guarded by three semilunar valves. They allow the blood to flow into systemic aorta only.
Functioning of heart Heart acts as a force pump and also as a suction pump. Contraction of heart is known as systole and relaxation is known as diastole. A systole and its following diastole constitute a heart beat. Relation between the size of the body and rate of heart beat of an organism → Smaller the size, faster the heart rate. This is because smaller the animal, the more it loses body heat due to higher surface area volume ratio, and therefore, increased heart rate distributes body heat faster. Human body, have higher metabolism for body growth and therefore, the faster heart rate keeps the ‘supply’ and ‘take off ’ of the metabolic substance in right quantity.
