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Cells Cell differentiation, Summaries of Biology

Biology

19. Differentiation is the generation of specialised cells which acquire different organelles to enable them to carry out specific functions.

Typology: Summaries

2021/2022

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GCSE Biology Cells Biology 1
Specialised cell
Function
Adaptations
7.
Red blood cell
Carries oxygen.
• Large surface area.
• Contains haemoglobin.
• No nucleus to create more space.
8.
White blood cell
Destroys microorganisms.
• Irregular shape to get out of blood vessels.
9.
Egg cell (ovum)
Join with sperm cell and provide
food for new cell formed.
• Large
• Contains lots of cytoplasm
10.
Sperm cell
Reach and join with egg cell.
• Long flagellum (tail) for swimming
• Enzymes of head to break into egg.
11.
Nerve cell
Carry nerve impulses to different
parts of the body.
• Long
• Connections at each end.
• Carry electrical signals.
12.
Muscle cell
Move the body.
• Contain protein fibres that contract.
• Large numbers of mitochondria.
13.
Ciliated cell
Move mucus.
• Thin layer of tiny cilia (moving hairs).
14.
Palisade cell
Absorb sunlight for
photosynthesis.
• Large surface area.
• Lots of chloroplasts.
15.
Root hair cell
Absorb water and minerals
• Large surface area.
16.
Xylem cell
Moves water through the plant.
• Made of dead cells.
• Thick, strengthened cellulose cell wall.
•
Hollow lumen.
17.
Phloem cell
Moves food through the plant.
• Made of living cells.
• Connected by sieve plates to form a tube.
Cells
1. Most animal cells have a nucleus, cytoplasm, membrane,
mitochondria and ribosomes.
2. Plant and algal cells also have a cell wall and often have
chloroplasts and a permanent vacuole.
3. Plant and animal cells are eukaryotic cells which have a
membrane, cytoplasm and a nucleus.
4. Bacterial cells are prokaryotic cells.
5. They are smaller than eukaryotic cells and have a cell wall,
membrane and cytoplasm, but do not have a nucleus.
6. Their genetic material is a single loop of DNA or several small
rings of DNA called plasmids in the cytoplasm.
Cell differentiation
18. Cells differentiate to form different types of cells. Animal cells differentiate at an early stage, whereas many plant cells can
differentiate throughout life.
19. Differentiation is the generation of specialised cells which acquire different organelles to enable them to carry out specific
functions.
20. Cells may be specialised to carry out a particular function.
21. Stem cells are unspecialised cells that can differentiate to form many different types of cells.
22. Stem cells from human embryos and adult bone marrow can be cloned and made to differentiate into different cells.
23. Stem cells may be used to treat paralysis and diabetes in the future.
24. In therapeutic cloning an embryo with the same genes as the patient is produced. Cells from this embryo will not be rejected
by the patient.
25. Risks e.g. transfer of viruses, a ssociated with the use of stem cells in medicine.
26. Stem cells from meristems in plants are used to produce clones quickly and cheaply.
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GCSE Biology Cells Biology 1

Specialised cell Function Adaptations

  1. Red blood cell Carries oxygen. (^) • Large surface area.
    • Contains haemoglobin.
    • No nucleus to create more space.
  2. White blood cell Destroys microorganisms. • Irregular shape to get out of blood vessels.
  3. Egg cell (ovum) Join with sperm cell and provide food for new cell formed. - Large - Contains lots of cytoplasm
  4. Sperm cell Reach and join with egg cell. (^) • Long flagellum (tail) for swimming
    • Enzymes of head to break into egg.
  5. Nerve cell Carry nerve impulses to different parts of the body.
    • Long
    • Connections at each end.
    • Carry electrical signals.
  6. Muscle cell Move the body. • Contain protein fibres that contract.
    • Large numbers of mitochondria.
  7. Ciliated cell Move mucus. (^) • Thin layer of tiny cilia (moving hairs).
  8. Palisade cell Absorb sunlight for photosynthesis.
    • Large surface area.
    • Lots of chloroplasts.
  9. Root hair cell Absorb water and minerals • Large surface area.
  10. Xylem cell Moves water through the plant. • Made of dead cells.
    • Thick, strengthened cellulose cell wall.
    • Hollow lumen.
  11. Phloem cell Moves food through the plant. (^) • Made of living cells.
    • Connected by sieve plates to form a tube.

Cells

  1. Most animal cells have a nucleus , cytoplasm , membrane , mitochondria and ribosomes.
  2. Plant and algal cells also have a cell wall and often have chloroplasts and a permanent vacuole.

3. Plant and animal cells are eukaryotic cells which have a

membrane, cytoplasm and a nucleus.

4. Bacterial cells are prokaryotic cells.

5. They are smaller than eukaryotic cells and have a cell wall,

membrane and cytoplasm, but do not have a nucleus.

6. Their genetic material is a single loop of DNA or several small

rings of DNA called plasmids in the cytoplasm.

Cell differentiation

  1. Cells differentiate to form different types of cells. Animal cells differentiate at an early stage, whereas many plant cells can differentiate throughout life.
  2. Differentiation is the generation of specialised cells which acquire different organelles to enable them to carry out specific functions.
  3. Cells may be specialised to carry out a particular function.
  4. Stem cells are unspecialised cells that can differentiate to form many different types of cells.
  5. Stem cells from human embryos and adult bone marrow can be cloned and made to differentiate into different cells.
  6. Stem cells may be used to treat paralysis and diabetes in the future.
  7. In therapeutic cloning an embryo with the same genes as the patient is produced. Cells from this embryo will not be rejected by the patient.

25. Risks e.g. transfer of viruses, associated with the use of stem cells in medicine.

26. Stem cells from meristems in plants are used to produce clones quickly and cheaply.

GCSE Biology Cells Biology 1

Culturing microorganisms

  1. Bacteria multiply by simple cell division ( binary fission ) as often as once every 20 minutes if they have enough nutrients and a suitable temperature.
  2. Bacteria can be grown in a nutrient broth solution or as colonies on an agar gel plate.
  3. Uncontaminated cultures of microorganisms are required for investigating the action of disinfectants and antibiotics.

Microscopes

  1. An electron microscope has a much higher magnification and resolution than a light microscope, so it can be used to study cells in much finer detail and show organelles.
  2. 𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟 𝑠𝑠𝑠𝑠𝑠𝑠𝑟𝑟 = (^) 𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑚𝑚𝑖𝑖𝑚𝑚𝑖𝑖^ 𝑚𝑚𝑠𝑠𝑖𝑖𝑖𝑖𝑠𝑠𝑚𝑚𝑖𝑖𝑖𝑖𝑚𝑚𝑚𝑚
  3. 1m = 1000mm
  4. 1mm = 1000μm (micrometre)
  5. 1μm = 1000nm (nanometre)
  6. To get smaller x 1000.
  7. To get bigger ÷ 1000.

Mitosis

  1. Chromosomes are found in the nucleus. They are made of DNA. Each chromosome carries a large number of genes.
  2. In body cells chromosomes are found in pairs.
  3. Mitosis occurs during growth or to produce replacement cells.
  4. During mitosis:
    • copies of the genetic material separate
    • the cell then divides once to form two genetically identical cells.

41. Mitosis forms part of the cell cycle.

Diffusion

  1. Substances can move into and out of cells across membranes by diffusion.
  2. Diffusion is the net movement of particles from an area of high concentration from an area of low concentration down a concentration gradient.
  3. Oxygen, carbon dioxide and urea passes through cell membranes by diffusion.
  4. Single celled organisms have a bigger surface area to volume ratio than multicellular organisms, so transfer sufficient substances across their surface.
  5. Multicellular organisms require specialised organ systems to exchange sufficient substances.

Osmosis

  1. Water may move across cell membranes by osmosis.
  2. Osmosis is the movement of water from a dilute solution (high concentration) to a more concentrated solution (low concentration) through a partially permeable membrane.
  3. An isotonic solution is one that is the same concentration as the cell.
  4. Water moves in and out at the same rate in an isotonic solution.
  5. A hypotonic solution has a higher concentration of water (low concentration of solutes) than the cell (low water and high solutes).
  6. Water moves into the cell until it reaches equilibrium (equal concentrations).
  7. A hypertonic solution has a lower concentration of water (high concentration of solutes) than the cell (high water and low solutes).
  8. Water moves out of the cell until it reaches equilibrium.
  9. Lysis – bursting an animal cell by osmosis.
  10. Crenation – shrinking an animal cell by osmosis.
  11. Turgid – A plant cell fully inflated with water.
  12. Flaccid – A plant cell that is limp through a reduction of pressure inside the cell (some water lost).
  13. Plasmolysed – a plant cell that has lost water causing the cell membrane to be pulled away from inside the cell wall.

Active transport

  1. Active transport involves the movement of ions or molecules from a low concentration to a high concentration against a concentration gradient on a cell membrane.
  2. Energy is required from respiration to move the substances.
  3. Mineral ions can be absorbed by active transport into plant root hairs from very dilute solutions in the soil.
  4. Sugar can be absorbed by active transport from the gut into the blood.

GCSE Biology Organisation Biology 2

Coronary heart disease

  1. Fatty material builds up in coronary arteries reducing blood flow to the heart muscle.
  2. Stents can be used to keep the coronary arteries open.
  3. Statins reduce cholesterol levels, so fatty material is deposited more slowly.
  4. Faulty heart valves can be replaced with biological or mechanical ones.
  5. Heart failure can be treated with a heart and lung transplant.
  6. Artificial hearts can be used whilst waiting for a transplant, or to allow the heart to rest and recover.

Blood

  1. Blood is a tissue consisting of plasma, red blood cells, white blood cells and platelets.
  2. Plasma transports dissolved chemicals and proteins around the body.
  3. Red blood cells transport oxygen attached to haemoglobin.
  4. White blood cells help to protect the body against infection.
  5. Platelets are fragments of cells involved in blood clotting.

Health issues

  1. Health is the state of physical and mental well- being.
  2. Factors such as diet, stress and life situations can have a serious effect on physical and mental health.
  3. Diseases are major causes of ill health.
  4. Different diseases may interact:
    • defects in the immune system increase the chance of catching an infectious disease.
    • Viral infections can trigger cancers.
    • Immune reactions can trigger allergies.
    • Physical ill-health can lead to depression and mental illness.

Lifestyle and health

  1. Various risk factors are linked to some non- communicable disease.
  2. These can be aspects of a person’s lifestyle or substances in the person’s body or environment.
  3. A causal mechanism has been proven for some risk factors but not in others:
  • The effects of diet, smoking and exercise on cardiovascular disease.
  • Obesity as a risk factor for type 2 diabetes.
  • The effect of alcohol on the liver and brain function.
  • The effect of smoking on lung disease and lung cancer.
  • The effects of smoking and alcohol on unborn babies.
  • Carcinogens, including ionising radiation, as risk factors in cancer.
  1. Many diseases are caused by the interaction of a number of factors.

Cancer

  1. Cancers ( malignant tumours ) result from uncontrolled cell division.
  2. Cancer cells may invade neighbouring tissues, or break off and spread to other parts of the body in the blood, where they form secondary tumours.

Plant organ system

  1. Plant organs include stems, roots and leaves.
  2. Organs are made up of different tissues, eg meristem tissue at growing tips.
  3. The leaf is the organ of photosynthesis.
  4. The roots, stem and leaves form a plant transport system.
  5. Root hair cells absorb water by osmosis and mineral ions by diffusion and active transport.
  6. Xylem tissue transports water and dissolved ions. The flow of water from the roots to leaves is called the transpiration stream.
  7. Xylem tissue is composed of hollow tubes strengthened with lignin.
  8. Phloem tissue transports dissolved sugars from the leaves to other parts of the plant. The movement of food through phloem is called translocation.
  9. Phloem cells have pores in their end walls for moving of cell sap.

Structure Function

GCSE Biology Infection and response Biology 3

Communicable diseases

  1. Communicable diseases are infectious diseases caused by pathogens.
  2. Pathogens may be viruses , bacteria , protists or fungi. They may infect plants or animals.
  3. Pathogens can be spread by direct contact, by water or by air.
  4. The spread of diseases can be reduced or prevented by: - simple hygiene measures - destroying vectors

• isolation of infected individuals

• vaccination

Viral disease

  1. Viral diseases include measles and AIDS, which is caused by HIV.
  2. Measles has symptoms of a fever and red skin rash.
  3. It is a serious illness that can be fatal if complications arise.
  4. Most young children are vaccinated against measles.
  5. The measles virus is spread by inhalation of droplets from sneezes and coughs.
  6. HIV initially causes a flu-like illness.
  7. Unless successfully controlled with antiretroviral drugs, the virus attacks the body’s immune cells.
  8. Late stage HIV infection, or AIDS, occurs when the body’s immune system becomes so badly damaged it can no longer deal with other infections or cancers.
  9. HIV is spread by sexual contact of exchange of bodily fluids such as blood, which occurs when drug users share needles.
  10. Tobacco mosaic virus (TMV) is a plant pathogen.
  11. It has a distinct mosaic pattern of discolouration on the leaves, which affects the growth of the plant due to lack of photosynthesis.
  12. Viruses enter cells and damage them to cause symptoms.
  13. Antibiotics don’t treat viruses as they cannot enter cells.

Bacterial disease

  1. Bacterial diseases include salmonella food poisoning and the sexually transmitted disease gonorrhoea.
  2. Salmonella food poisoning is spread by bacteria ingested in food or on food prepared in unhygienic conditions.
  3. In the UK, poultry are vaccinated against Salmonella to control the spread.
  4. Fever, abdominal cramps, vomiting and diarrhoea are caused by the bacteria and toxins that they excrete.
  5. Gonorrhoea is a sexually transmitted disease with symptoms of a thick yellow or green discharge from the vagina or penis and pain when urinating.
  6. It was easily treated with the antibiotic penicillin until many resistant strains appeared.
  7. The spread of gonorrhoea can be controlled by antibiotic treatment and the use of a barrier method of contraception such as a condom.

Fungal disease

  1. Humans can also be infected with fungal diseases.
  2. Rose black spot is a fungal disease where purple or black spots develop on leaves, which turn them yellow and makes them drop off early.
  3. It affects the growth of plants as photosynthesis is reduced.
  4. It is spread in the environment by wind or water.
  5. It can be treated by using fungicides and /or removing and destroying the affected leaves.

Protist disease

  1. Malaria is caused by a protist transmitted by mosquitos.
  3. Malaria causes recurrent episodes of fever and can be fatal.
  4. Spread of malaria is controlled by preventing the vectors (mosquitos) from breeding and by using mosquito nets to avoid being bitten.

GCSE Biology Infection and response Biology 3

Monoclonal antibodies

  1. Monoclonal antibodies (MAB) are produced from a single clone of cells. They are specific to one antigen , so target a specific chemical or cell in the body.
  2. A lymphocyte that makes a specific antibody is combined with a tumour cell to form a hybridoma cell. This is cloned to produce many identical cells which all produce the specific antibody.
  3. There are many uses for MABs:
  • Diagnosis in pregnancy tests.
  • In labs to measure the levels of hormones and other chemicals in the blood or to detect pathogens.
  • In research to locate and identify specific molecules in a cell or tissue by binding them with a fluorescent dye.
  • To treat diseases: for cancer the monoclonal antibody can be bound to a radioactive substance, a toxic drug or a chemical which stops cells growing and dividing. It delivers the substance to the cancer cells without harming other ells.
  1. MABs can have more serious side effects than expected.
  2. They are not as widely used as everyone hoped when they were first developed.

Plant diseases

  1. Plants can be infected by a range of viral, bacterial and fungal pathogens as well as by nematode worms and insects.
  2. Tobacco mosaic virus affects many plants, eg tomatoes.
  3. Rose black spot is a fungal disease spread by water or wind.
  4. Aphids feed on the sap of plants and affect plant growth.
  5. Ion deficiencies can damage plants, eg stunted growth by nitrate deficiency and chlorosis by magnesium deficiency.

Detecting plant diseases

  1. Plant diseases can be detected by:
    • stunted growth
    • spots on leaves
    • areas of decay (rot)
    • growths
    • malformed stems or leaves
    • discolouration
    • presence of pests.
  2. Identification can be made by:
    • Using a gardening manual.
    • Taking infected plants to a lab.
    • testing kits that use monoclonal antibodies.

Ion deficiency

  1. Plants can be damaged by a range of ion deficiency conditions.
  2. Nitrate deficiency causes stunted growth.
  3. Nitrate is needed for protein synthesis and therefore growth.
  4. Magnesium deficiency causes chlorosis (yellowing of the leaves).
  5. Magnesium ions are needed to make chlorophyll.

Plant defence responses

  1. Plants have physical and chemical defence responses to resist the invasion of microorganisms.
  2. Physical defences include: cellulose cell walls, tough waxy cuticles on leaves; layers of dead cells around stems (bark on trees) which fall off.
  3. Chemical defence responses include: antibacterial chemicals and poisons to deter herbivores.
  4. There are also mechanical adaptations to deter animals from eating or touching them.
  5. Mechanical adaptations include: thorns and hairs to deter animals; leaves which droop or curl when touched; mimicry to trick animals.

GCSE Biology Bioenergetics Biology 4

Photosynthesis

  1. Carbon dioxide + water  glucose + oxygen.
  2. 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O (^2)
  3. Photosynthesis takes place in the palisade cells in the leaf.
  4. Photosynthesis is an endothermic reaction in which energy is transferred from the environment into the chloroplasts by light.

Rate of photosynthesis

  1. The rate of photosynthesis may be limited by:
    • low temperature
    • shortage of CO 2
    • shortage of light
    • shortage of chlorophyll.
  1. When the graph has a slope, the investigated factor is limiting.
  2. When the slope levels out, another factor has started to limit photosynthesis.
  3. The rate of photosynthesis can be measured by counting the number of oxygen bubbles produced by a plant in water.
  4. Factors that can limit the rate of photosynthesis are called limiting factors.
  5. Limiting factors are important economically in greenhouses. They help us work out the optimum conditions for growing plants.
  6. Glucose produced in photosynthesis may be:
    • used for respiration
    • converted into starch for storage
    • used to produce fats and oils for storage or cellulose to strengthen cell walls
    • used to produce amino acids for protein synthesis.

Respiration

  1. Respiration can take place aerobically or anaerobically to transfer energy.
  2. Respiration is an exothermic reaction.
  3. Respiration takes place in the mitochondria.
  4. Organisms need energy for chemical reactions, movement and to keep warm. Aerobic respiration
  5. During aerobic respiration glucose and oxygen react to release energy.

18. Glucose + oxygen  carbon dioxide + water.

19. C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O

Anaerobic respiration

  1. Anaerobic respiration is the incomplete oxidation of glucose so less energy is released than in aerobic respiration.

21. In muscle cells: Glucose  lactic acid

22. C 6 H 12 O 6  2C 3 H 6 O 3

  1. In some plant and yeast cells:

Glucose  ethanol + carbon dioxide

24. C 6 H 12 O 6  2C 2 H 5 OH + 2CO 2

  1. Anaerobic respiration in yeast cells is called fermentation and has economic importance in the manufacture of bread and alcoholic drinks.

light light

Response to exercise

  1. During exercise the heart and breathing rates increase and breath volume increases to supply oxygen to muscle cells faster.
  2. Muscle cells can respire anaerobically if there is insufficient oxygen. This produces lactic acid and creates an oxygen debt.
  3. Lactic acid can cause muscle fatigue. The cells stop contracting efficiently.
  4. When exercise stops, the oxygen debt must be repaid by continuing to breathe deeply.
  5. Blood transports lactic acid to the liver where it is converted back into glucose.
  6. The oxygen debt is the amount of oxygen needed to oxidise lactic acid.

Metabolism

  1. Metabolism means all the chemical reactions happening in a living organism.
  2. Metabolism includes:
    • the conversion of glucose to starch, glycogen and cellulose
    • the formation of lipids
    • the formation of amino-acids and proteins
    • respiration
    • the breakdown of excess proteins to form urea for excretion.

GCSE Biology Homeostasis and response – Biology only Biology 5

Control of body temperature

  1. Body temperature is monitored and controlled by the thermoregulatory centre in the brain. It has receptors sensitive to the temperature of the blood.
  2. Temperature receptors in the skin send impulses to the thermoregulatory centre.
  3. If the body temperature is too high, blood vessels dilate ( vasodilation ) and sweat is produced from skin glands.
  4. Sweat cools the body as it evaporates from the skin.
  5. If the body temperature is too low, blood vessels constrict ( vasoconstriction ), sweating stops and skeletal muscles contract ( shiver ).

Maintaining water and nitrogen balance

  1. Water leaves the body via the lungs during exhalation.
  2. Water, ions and urea are lost from the skin in sweat.
  3. There is no control over water, ion or urea loss by the lungs or skin.
  4. Excess water, ions and urea are removed via the kidneys in the urine.
  5. If body cells lose or gain too much water by osmosis they do not function efficiently.
  6. Urea is produced in the liver by the breakdown of excess amino acids.
  7. In the liver, amino acids are deaminated to form ammonia.
  8. Ammonia is toxic and is immediately converted to urea for safe excretion.

Kidneys

  1. The kidneys produce urine by filtration of the blood and selective reabsorption of useful substances.
  2. All the sugar and dissolved ions needed by the body and as much water as the body needs are selectively reabsorbed.
  3. Urea, excess ions and water are excreted in urine.
  4. ADH is released by the pituitary gland when the blood is too concentrated. It causes more water to be reabsorbed back into the blood.
  5. ADH control of water in the blood is an example of negative feedback.
  6. Kidney failure can be treated by kidney transplant or by using kidney dialysis.
  7. Kidney dialysis is a procedure to remove waste products and excess fluid from the blood.
  8. Blood is diverted to a machine to be cleaned and pumped back into the body.

Plant hormones

  1. Hormones control and coordinate growth and responses to light and gravity in plants.
  2. Auxin is a powerful growth hormone produced naturally by plants.
  3. Responses to light and gravity are controlled by the unequal distribution of auxin which causes unequal growth rates in shoots and roots.
  4. Auxin moves away from the light which makes that part of the shoot grow. It makes the stem grow towards the light.
  5. Gibberellins are important in initiating seed germination.
  6. Ethene controls cell division and ripening of fruits.

Plant hormones

  1. Plant hormones are used in agriculture and horticulture.
  2. Auxins are used as weed killers,, as rooting powders and for promoting growth tissue culture.
  3. Giberellins can be used to end seed dormancy, promote flowering and increase fruit size.
  4. Ethene is used in the food industry to control the ripening of fruit during storage and transport.

GCSE Biology Homeostasis and response Biology 5

Homeostasis

  1. Homeostasis is the regulation of internal conditions to maintain optimal conditions for enzyme action and cell function.
  2. Automatic control systems involve nervous responses and chemical responses.

3. Control systems have receptors , a coordination centre and

effectors.

Human endocrine system

  1. The system is composed of endocrine glands that secrete hormones into the blood to be carried to a target organ where it has an effect.
  2. The pituitary is the master gland. It secretes many hormones that affect other glands.
  3. Hormones are chemical messengers.

Nervous system

  1. The functions of the nervous system are to detect and react to stimuli ; to coordinate behaviour.
  2. The structure of the central nervous system (CNS): receptors ; different types of neurones , coordinator (brain or spinal cord); effectors , synapses.
  3. Sensory neurones carry impulses (electrical signals) from the sense organ to the relay neurone.
  4. The relay neurone carries electrical impulses in the CNS.
  5. The motor neurone carries electrical impulses from the relay neurone to the muscle or gland ( effector ) to make it respond.
  6. Neurones line up end to end throughout the CNS.
  7. Synapses are the gaps between each neurone.
  8. Electrical impulses cannot cross a synapse.
  9. At the end of the neurone, the electrical impulse causes a chemical to be released.
  10. The chemical diffuses across the synapse and triggers an electrical impulse in the next neurone.
  11. Diffusion of the chemical is slower than the electrical impulse.

Reflex arc

  1. Some of your reactions happen without you thinking about them, e.g. moving your hand when you touch something hot. These are called reflex actions.
  2. Reflex actions are automatic and rapid to protect the body from harm.
  3. A stimulus is a change in the environment that can be detected by the body.
  4. A receptor is a cell that detects the stimulus.
  5. The effector is the area that makes the response.
  6. The reflex action is a reflex arc that doesn’t involve the brain, it is very fast.
  7. The brain is informed after the action has happened.

GCSE Biology Inheritance, variation and evolution Biology 6

Sexual and asexual reproduction

  1. Sexual reproduction involves the joining ( fusion ) of male and female gametes (sperm and egg ) in animals and pollen and ovule cells in flowering plants.
  2. This mixing of genetic information leads to variation in the offspring.
  3. Only mitosis is involved.
  4. Gametes are produced by meiosis.
  5. Asexual reproduction involves only one parent and no fusion of gametes.
  6. There is no mixing of genetic information.
  7. This leads to genetically identical offspring ( clones ).

Meiosis

  1. Cells in reproductive organs divide by meiosis to form gametes.
  2. When a cell divides to form gametes: copies of the genetic information are made and the cell divides twice to form four gametes, each with a single set of chromosomes.
  3. All gametes are genetically different from each other.
  4. Gametes join at fertilisation to restore the normal number of chromosomes. The new cell divides by mitosis, and as the embryo develops, cells differentiate.

DNA and the genome

  1. DNA is a polymer made up of two strands forming a double helix.
  2. DNA is found in chromosomes in the nucleus of a cell.
  3. A gene is a small section of DNA.
  4. Each gene codes for a sequence of amino acids to form a particular protein.
  5. The genome is all the genetic material of an organism.

17. The human genome has been studied and will be

important for medicine in the future.

Genetic inheritance

  1. A gamete is the male or female sex cell which contains the genetic information.
  2. Some characteristics are controlled by a single gene. Each gene may have different forms called alleles.
  3. The genes present, or genotype , operate at a molecular level to develop characteristics that are expressed as a phenotype.
  4. A dominant allele is expressed if only present on one chromosome.
  5. A recessive allele is only expressed if present on both chromosomes.
  6. If the two alleles present are the same the person is homozygous for that trait, but if the alleles are different they are heterozygous.
  7. ‘Homo’ means the same. ‘Hetero’ means different.
  8. Most characteristics are a result of multiple genes interacting.
  9. Some disorders are inherited, eg polydactyly (caused by a dominant allele) and cystic fibrosis (caused by a recessive allele).
  10. A Punnett square can be constructed to predict the outcome of a monohybrid cross.

Sex determination

  1. Human body cells contain 23 pairs of chromosomes.
  2. 22 pairs control characteristics only.
  3. The 23rd^ pair carries the genes that determine sex.
  4. In females the sex chromosomes are the same (XX).
  5. In males the chromosomes are different (XY).

GCSE Biology Inheritance, variation and evolution Biology 6

Genetic engineering

  1. Genetic engineering involves modifying the genome of an organism to introduce a desired characteristic.
  2. Genes can be cut from the chromosome of a human or other organism and transferred into the cells of other organisms.
  3. Enzymes are used to cut the gene from a chromosome.
  4. The gene is inserted into a vector , eg bacterial plasmid or virus.
  5. The vector is used to insert gene into cell.
  6. The cell then makes a new protein to produce the desired characteristic.
  7. Examples of genetic engineering are: weed killer resistance soya beans; golden rice; humalin (insulin made in bacteria).
  8. Concerns about GM crops, eg effect on populations of wild flowers and insects, and uncertainty about safety of eating them.

Variation

  1. Differences in the characteristics of individuals may be due to:
    • genes they have inherited
    • environmental causes
    • a combination of genetic and environmental causes.
  2. There is usually extensive genetic variation within a population of a species.
  3. All variants arise from mutations.
  4. Most mutations have no effect on the phenotype.
  5. Some mutations influence phenotype.
  6. A few mutations determine the phenotype.
  7. Mutations occur continuously but it is only very rarely that a mutation leads to a new phenotype.
  8. If the phenotype is suited to an environmental change, it can lead to a relatively rapid change in the species.

Selective breeding

  1. Selective breeding ( artificial selection ) is the process by which humans breed plants and animals for useful characteristics.
  2. Selective breeding of food plants has produced disease or weather resistant crops, more attractive or better flavoured fruits and crops that are easier to harvest.
  3. Selective breeding of animals has produced cows that produce more milk, animals that produce more, better flavoured or leaner meat.
  4. Selective breeding can lead to inbreeding , where some breeds are particularly prone to disease or inherited defects. Some breeds of dogs suffer from inbred defects.

Evolution

  1. Darwin’s theory of evolution by natural selection states that all species evolved from simple life forms that first developed more than three billion years ago.
  2. Characteristics favourable to the environment are passed on because the animal is more likely to survive and reproduce.
  3. Mutations are changes in the DNA code. They may lead to more rapid evolution, although mutations resulting in a new phenotype are rare.
  4. Organisms of the same species can interbreed to produce fertile offspring.

Evidence for evolution

  1. The theory of evolution by natural selection is now widely accepted. At the time, it contested with religious belief.
  2. Fossils are the ‘remains’ of organisms from many years ago, which are found in rocks.
  3. Scientists can’t be certain about how life began on Earth as many early forms of life were soft- bodied, so few traces remain. What traces there were have been destroyed by geological activity.
  4. Fossils show how much, or how little, organisms have changed over time.
  5. Bacteria can evolve rapidly because they reproduce at a fast rate.
  6. Mutations produce new strains. Resistant strains are not killed by antibiotics, so they survive and reproduce. Resistant strains spread because people are not immune and there is no effective treatment.
  7. MRSA is resistant to antibiotics.

Extinction

  1. Extinction may be caused by:
    • changes to the environment over geological time
    • new predators
    • new diseases
    • new, more successful competitors
    • a single catastrophic event, eg massive volcanic eruptions or collisions with asteroids.

GCSE Biology Ecology Biology 7

Classification

  1. Traditionally organisms have been classified into groups depending on their structure and characteristics.
  2. Classification can be described by: Kingdom; Phylum; Class; Order; Family; Genus; Species.
  3. Organisms were classified into smaller and smaller groups.
  4. Carl Linnaeus studied the similarities and differences between organisms to classify them. He developed the binomial system to name organisms by genus and species.
  5. Today powerful microscopes are used to see internal structures. This and biochemical analysis has led to new classification systems.
  6. Carl Woese developed the three domain system to classify organisms as:
  • Archaea (primitive bacteria)
  • Bacteria (true bacteria)
  • Eukaryota (protists, fungi, plants and animals).

Communities

  1. An ecosystem is the interaction of a community of living organisms ( biotic ) within the non-living ( abiotic ) parts of their environment.
  2. Organisms need a supply of materials from their surroundings and other organisms to survive and reproduce.
  3. Plants compete for light, space, water and mineral ions.
  4. Animals compete for food, mates and territory.
  5. One species depends on others for food, shelter, pollination, seed dispersal etc. This is called interdependence.
  6. A stable community is one where all the species and environmental factors are in balance so that population sizes remain fairly constant.

Biotic and abiotic factors

  1. Biotic factors are living factors that can affect a community:
    • availability of food
    • new predators arriving
      • new disease organisms
      • one species out-competing another so the numbers are no longer sufficient to breed.
  2. Abiotic factors are non-living factors which can affect a community:
    • light intensity
    • temperature
    • moisture levels
    • soil pH and mineral content
    • wind intensity and direction
    • carbon dioxide levels for plants

Sampling • oxygen levels for aquatic animals

  1. Quantitative data on the distribution and abundance of organisms can be obtained by:
  • random sampling with quadrats
  • sampling along a transect.

Adaptations

  1. Organisms have adaptations for survival; they may be structural, behavioural or functional.
  2. Extremophiles can survive in very extreme environments, such as high temperature or pressure, or in high salt concentration.

Food chains

  1. Feeding relationships can be represented by food chains.
  2. A food chain begins with a producer which synthesises molecules, which is usually a green plant or alga which makes glucose by photosynthesis.
  3. Producers are eaten by consumers.
  4. Consumers that eat other animals are predators , and those eaten are prey.
  5. In a stable community the numbers of predators and prey rise and fall in cycles.

Biodiversity

  1. Biodiversity is the variety of all life on Earth.
  2. A great biodiversity ensures stability of ecosystems.
  3. The future of the human species relies on us maintaining a good level of biodiversity.
  4. Human activities can reduce biodiversity and we should try to stop this.

GCSE Biology Ecology Biology 7

Material recycling

  1. Materials are recycled to provide the building blocks for future organisms.
  2. The carbon cycle returns carbon to the atmosphere as carbon dioxide and mineral ions to the soil.
  3. The water cycle provides fresh water for plants and animals on land before draining into the seas. Water is continuously evaporated and precipitated.

Waste management

  1. Rapid growth in the human population means more resources are used and more wastes are produced, which could lead to more pollution.
  2. Pollution kills plants and animals which can reduce biodiversity.
  3. Waste may pollute water with sewage, fertilisers or toxic chemicals.
  4. Waste may pollute air with smoke and gases such as sulfur dioxide, which contributes to acid rain.
  5. Waste may pollute land with toxic chemicals such as pesticides and herbicides , which may be washed from the land into water.

Land use and deforestation

  1. Humans reduce the amount of land available for other plants and animals by building, quarrying, farming and dumping waste.
  2. The destruction of peat bogs to produce compost releases carbon dioxide into the atmosphere. It destroys habitats and reduces biodiversity.
  3. Large scale deforestation occurred to:
    • provide land for cattle and rice fields to provide more food
    • grow crops from which biofuel can be produced.
  4. This destruction of large areas of trees has:
    • increased the release of carbon dioxide by burning and microbial activity
    • reduced the rate at which carbon dioxide is removed from the atmosphere by photosynthesis to be ‘locked up’ in wood
    • led to a reduction in biodiversity.

Global warming

  1. Levels of carbon dioxide and methane in the atmosphere are increasing and contribute to global warming.
  2. Consequences of global warming include:
    • loss of habitat when low lying areas flood
    • changes in the distribution of species where temperature of rainfall changes
    • changes in migration patterns.

Programmes

  1. Programmes have been put in place to reduce the negative effects on ecosystems and biodiversity.
  • breeding programmes for endangered species
  • protection and regeneration of rare habitats, eg coral reefs, mangroves, heathland
  • reintroduction of field margins and hedgerows in agricultural areas
  • reduction of deforestation and carbon dioxide emissions by some governments
  • recycling resources rather than dumping waste in landfill.