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Unit 2 Summary Notes
Cells, tissues and organs
Multicellular organisms contain many different types of cells, which are specialised to carry
out particular functions. A large number of specialised cells together make up tissues and
various tissues together make up an organ.
Specialised animal cells
There are numerous specialised cells in animals which perform particular functions.
Some examples of specialised animal cells and their functions are described below.
Muscle cells
These are long, thin cells which contract to cause movement. The cells contain a large
number of mitochondria to produce the large amount of energy required for this contraction.
Sperm cells
A sperm cells particular function is to fertilise an egg cell. It has a specialised tail to allow it
to swim towards an egg and the head of the sperm cell contains enzymes to digest the
exterior of the egg, which allows the sperm to enter the egg and fuse
with it.
Nerve cells
These cells form connections with other nerve cells to create a huge network which is used
to transmit impulses throughout the body; this allows us to co-ordinate movement and
thoughts. They have long projections which allow them to make connections with other cells;
these connections can be made with cells some distance away.
Blood cells
Red blood cells are small and have a ‘bi-concave’ shape to increase their
surface area and to allow them to squeeze through tiny blood capillaries. Their
function is to transport oxygen around the body; to achieve this, they contain
a pigment called haemoglobin which binds with oxygen and they lack a nucleus to maximise
the amount of pigment they can carry.
Head contains
nucleus and enzymes
Tail
Projection to connect
with other cells
White blood cells fight infection in the body. They have an irregular shape to squeeze
through blood vessels and their shape allows them to surround a microbe; they also contain
enzymes which digest the microbe into harmless waste substances.
Specialised plant cells
Phloem cells
These cells are involved in the transport of sugar in plants; they have
perforated end walls which allow sugars to be transported to the next phloem
cell. They also possess companion cells with a large nucleus to control the
phloem cells.
Root hair cells
These cells are responsible for absorbing water (for
photosynthesis) from soil around the roots. Each cell has a large
surface area to maximise the volume of water it can absorb.
Palisade mesophyll cells (leaf cells)
These are found in the upper layer of a leaf and have the main function of carrying out
photosynthesis; they contain a very large number of chloroplasts to maximise
photosynthesis.
Tissues
Tissues are groups of specialised cells which will carry out a particular function.
Examples of animal tissues include:
-Muscle -Blood -Nerves
Examples of plant tissues include:
-Vascular tissue (i.e. transport tissues such as xylem and
phloem)
-Palisade tissue (layer of palisade cells within the leaf)
-Root tissue
Organs
Organs are made up of several types of tissue grouped
together, for example, the small intestine is made up of muscle
tissue, connective tissue, epithelial lining tissue and also nerve
tissue to control its action. Organs can carry out specific
function due to the large variety of specialised cells within
them.
Potential uses of stem cells
Stem cells are currently being used after cancer treatment to restore destroyed stem cells;
bone marrow (which contains stem cells) is transplanted into a patient and the cells it
contains will begin to produce blood cells.
Due to the unspecialised nature of stem cells, they could potentially be used to cure or
repair damage caused by a wide range of conditions.
Stem cell technology could be used to:
repair damaged heart tissue after a heart attack
grow new skin cells to repair skin damage after burns
grow complete organs (removing the need for waiting lists for transplants)
Stem cell technology is a promising but ethically controversial procedure due to the source
of some stem cells; stem cells can be derived from adult tissues (and other sources) or they
can be sourced from embryos. The use of embryonic stem cells has been criticised by many
groups due to the ethics of creating, using and destroying potential embryos.
Part b: Meristems
Within plants, only particular areas can undergo mitosis and therefore contribute to growth,
these areas are called meristems. Meristems produce non-specialised cells in plants and
these non-specialised cells can potentially become any type of plant cell (e.g. leaf mesophyll
cells, phloem cells etc).
Areas which undergo growth, such as root tips and shoot tips, will contain meristems.
Root tip
Shoot tip
2.2. - Propagating and Growing Plants Summary
GGrroowwiinngg PPllaannttss ffrroomm SSeeeedd TTyyppeess ooff SSeeeeddss
SSoowwiinngg SSeeeeddss
Seeds must be sown in a particular way to allow the best chance of growth. They must:
Be spread evenly
Watered regularly
Be maintained at an appropriate temperature (using a thermostat) and humidity.
VVeeggeettaattiivvee PPrrooppaaggaattiioonn
VVeeggeettaattiivvee pprrooppaaggaattiioonn iiss aa ffoorrmm ooff aasseexxuuaall rreepprroodduuccttiioonn uusseedd bbyy ppllaannttss wwhhiicchh pprroodduucceess cclloonnee ooffffsspprriinngg.. TThheerree aarree mmaannyy mmeetthhooddss ooff vveeggeettaattiivvee rreepprroodduuccttiioonn,, eexxaammpplleess ooff wwhhiicchh aarree oouuttlliinneedd bbeellooww..
BBuullbbss aanndd TTuubbeerrss Bulbs store food. They have buds which produce flowers or daughter bulbs. Since these are produced from one parent , this is a method of vegetative propagation. The food store allows bulbs to withstand winter conditions and to grow early in the spring before seeds germinate.
Type of seed Method of sowing^ Advantage
Large seeds
(e.g. broad bean)
Individually
spread out
Reduces competition
for light, water,
space and minerals
Very small seeds
Mixed with sand Helps to sow the seeds more evenly
Pelleted (enclosed in a ball of clay)
Seeds are easier to handle and can be
sown more evenly
Chitted seeds
(pre-germinated)
Individually
spread out
Seed coat split to
allow germination before sowing
plantlet
2. Production of Leaf Plantlets The Mexican Hat Plant produces large numbers of small plantlets along the leaf edges. These can be detached from the leaf and grown in pots of compost.
The Piggy -back Plant produces plantlets in the middle of its leaves.
3. Production of Plants from Offsets
Some plants, for example Mother-in-Law’s Tongue, produce offsets. Offsets are small plantlets produced as side shoots at the base of the parent plant.
These can be detached from the parent plant and grown separately.
AArrttiiffiicciiaall PPrrooppaaggaattiioonn
AArrttiiffiicciiaall pprrooppaaggaattiioonn iiss aa mmeetthhoodd ooff pprrooppaaggaattiinngg ppllaannttss wwhhiicchh iiss ccaarrrriieedd oouutt bbyy hhuummaannss;; tthhiiss ttyyppee ooff pprrooppaaggaattiioonn iiss nnoott aa nnaattuurraall mmeetthhoodd uusseedd bbyy ppllaannttss.. Artificial propagation means that part of a plant, for example a stem or leaf, is cut off from its parent and treated so that it grows into a new plant.
This method is quicker than waiting for the parent plant to produce seeds and all new plants will be exactly like the parent plant e.g. same colour of flower and leaves.
MMeetthhooddss ooff aarrttiiffiicciiaall pprrooppaaggaattiioonn aarree ddeessccrriibbeedd bbeellooww..
1. Taking Stem Cuttings
Nodes are points on a plant's stem where new growth occurs. When a plant stem is wounded , for example by cutting below a node, the stem produces roots. Rooting powder can also be used which speeds up root growth
Mother of Thousands
plantlet s
offset
Cuttings are placed in propagators , these have electrical cables that supply heat to the cuttings to encourage root growth.
If too much heat is supplied, the plant will wilt as it loses too much water. This can be prevented by reducing the leaf surface area by removing some of the lower leaves or by increasing the humidity by placing the cutting in a propagator or covering it with a polythene bag.
Commercial plant growers use mist propagation to maintain a high level of humidity in the air around the cuttings by continually spraying a very fine mist of water into the air.
Taking a Cutting
2. Layering
Layering is a method of propagating plants which have long flexible stems.
When the stem is still attached to the parent plant, it is 'pegged down' into a pot of rooting compost or into the soil if it is an outdoor plant. Often the stem is wounded by cutting below a ' node ' (point where leaves are attached) and dusted with rooting powder to encourage root growth.
Step 1 A diagonal cut is made in the stem
just below a node (i.e. where leaf joins the stem).
Step 2 Remove the lower leaves of the
cutting to reduce water loss.
Step 3 Dip the cut end of the stem into rooting
powder to encourage the growth of roots.
Step 4 Carefully place the cutting into a hole in the
centre of compost in a plant pot. Gently firm the compost by pressing down around the cutting.
Step 5 Water the compost.
Step 6 Place the potted cutting in a propagator with a lid to
increase humidity and reduce water loss from the cutting.
Ventilation is also important in controlling temperature and humidity (how much moisture is in the air). To provide the best conditions for plant growth, automatic ventilation is essential. Automatic systems work without anyone being there to operate them. The two main automatic systems for controlling ventilation are automatic window openers and thermostatically controlled electric fans.
2 2.. FFllooaattiinngg FFleleeeccee aanndd CClloocchheess
Floating fleece and cloches also protect plants from the weather.
Cloches are tent-like structures made from glass, plastic or polythene. Plastic or polythene cloches are the most common type nowadays being cheaper and less likely to break than glass. Floating fleece is a light material which allows the plants to grow under it, protecting the plants from frost while still allowing water and light to pass through.
Commercial uses of plants
Plants are used for many different things and have become an enormous industry, on which
the entire world depends.
Some of the most common uses for plants are:
Food
Raw materials
Medicine
Fuels
Food
Agriculture or the production of plants for use as a food stuff, vital industry for all people in
the world. Of the land on planet earth, almost 40% is currently used for the production of
crops for food and there is the potential for even more land to be used in this way.
Corn – A staple food for the majority of sun-Saharan Africa, corn is both easily grown and is
edible with very little preparation.
Wheat – Covers more of the earth than any other crop and grows well in almost all climates
making it a better general crop than rice or corn. Wheat is also the major source of
vegetable protein for humans
Rice – A staple crop for the majority of Asia and is more important than corn as rice’s sole
use is as a food (corn has other used which will be discussed later). Rice accounts for 1/5 of
all the calories consumed by humans.
Raw Materials
The most obvious use of plants as raw materials is Timber wood, used to make frames for
buildings, buildings themselves, boats and any number of smaller items made from wood. Oils
extracted from plants (sunflower oil) can be used for things such as cooking. One of the
most used plants is the cotton plant, which is used to make clothes for people all over the
world.
Medicines
Another common commercial use for plants is in medicine. Some of the most well-known
medicines are mass produced in this way, for example:
Willow trees are used to produce Aspirin for helping with pain (among other things).
Opium poppies are used to produce morphine , a very strong pain killer.
Quinine made from the bark of Cinchona tree, is used to treat malaria.
Fuels
Corn is mass produced to make ethanol , which when mixed with gasoline, is used as gasohol.
Sugar cane is also grown for this use, in particular in South America and Australia.
The increasing population of the world has put greater demand on the production of plants in
particular the use of plants as food stuffs is incredibly important. As the population
increases, more forward planning and attention must be paid to the conservation and
management of plant species.
Pharming techniques
Pharming techniques involve the genetic modification of plants in order to improve the plant
yields or the development of new products.
This process involves the inserting of a gene into an existing plant species in order to create
an improved variety of that species. An example of this is the insertion of pesticide
resistance into oil seed rape plants, therefore less plants will be lost as waste.
An example of an organism that reproduces asexually is yeast.
Yeast reproduce by a process called budding.
Asexual Reproduction in Multicellular Organisms
Organisms such as some plants can reproduce asexually. There are various structures
produced by plants to allow them to reproduce by this method such as runners (strawberry
plants) , tubers (potato plants) and bulbs (daffodils).
Sexual Reproduction in Multicellular Organisms
In plants sexual reproduction results in the production of seeds which develop into new
plants.
The male sex cells in plants are called pollen grains and produced by the anthers and the
female gametes are called ovules and produced by the ovary.
Structure of a flowering plant
Name of Part Function Food Store Provides material and energy for growth of new plant Embryo Grows into a new plant Seed Coat Protects the seed
Bud forming on
the single celled
yeast
Embryo
Seed Coat
Food Store
anther
stamen
ovules
stigma ovary
Name of Structure Function of Part Stamen Male part of flower made up of the filament and the anther Anther Produces pollen grains, which contain the male gamete. Stigma Female part of the flower.Traps^ pollen grains on its sticky surface. Ovary Produces ovules Ovules Contain the female gametes
Pollination and Fertilisation Pollination Pollination is the transfer of pollen from the anther to the stigma. This can be performed by either wind or insects.
In wind pollinated flowers Flowers are small without bright petals, scent or nectar Anthers hang outside flower so that pollen is blown away by wind Feathery stigmas hang outside flower so that they can catch pollen blown in the wind Pollen grains are light and smooth so that they are blown easily away
In insect pollinated flowers Flowers large with bright petals, scent and nectar to attract insects Anthers and sticky stigma inside flower so that insect brushes against them Pollen grains are rough or sticky to catch onto insect.
Fertilisation When a pollen grain lands on the stigma during pollination a sugary substance on the surface causes it to grow a pollen tube.
The pollen tube grows down into the ovary. The male sex cell nucleus then leaves the pollen grain and travels down the pollen tube into the ovary to reach the female sex cell nucleus.
male sex cell nucleus
female sex cell nucleus
There are two methods of fertilisation – internal , mainly used by land animals, and external
used by aquatic animals. Internal fertilisation is where the sperm and egg join inside the
female. With external fertilisation the sperm and eggs are released into the surrounding
water where they join.
Examples of animals that use external
fertilisation are fish and amphibians.
Examples of animals that use internal
fertilisation are birds and mammals.
Development
In mammals internal development occurs, which means that the
embryo develops inside the female’s reproductive system.
Compared with bird development this has a number of advantages
such as the developing embryos are kept warm , fed and protected
by one or both parents.
In birds their eggs have to be incubated because they need to be
kept warm for the embryos to develop. After the eggs hatch, parental care of the young is
essential because they cannot fly or feed themselves at first.
Egg cell
(Female sex cell)
Sperm cell
(Male sex cell)
Fertilisation
Fertilised Cell
In trout the fertilised eggs begin to develop and when they hatch the trout fry feed on food
from their yolk sac. Once they are free-swimming and the mouth has developed they feed
on small aquatic animals.
Increasing Chances of Survival
Animals which have external fertilisation, e.g. trout and frogs , produce a great many more
eggs than animals which fertilise internally, e.g. birds and mammals.
With internal fertilisation there is a greater chance of sperm reaching the eggs and
fertilisation taking place. There is also less chance of the gametes becoming diseased. With
external fertilisation many of the eggs will get eaten by predators or will not get fertilised
as the sperm and eggs drift away from each other. As there is a greater chance of survival
with internal fertilisation, it is possible to produce fewer eggs.
Land animals need to use internal fertilisation so that the sperm can swim to the egg or, as in
the case of amphibians, return to the water to breed.
As mammals also have internal development and look after their young after birth, this
means that they can produce even fewer eggs than other groups of animals.
The number of young surviving can be calculated using the following formula:
Number of = fertilised eggs – (diseased eggs + eggs eaten + young eaten)
young surviving
The percentage of the young surviving can be calculated using the following formula:
% = Total young surviving x 100
Total number of eggs produced
Examples of the survival chances of different species
Species Total no.
eggs
produced
No. of
eggs
fertilised
No. of
fertilised
eggs
diseased
No. of
fertilised
eggs
eaten
No. of
young
eaten
Total
young
surviving
% survival
Rabbit 8 8 0 0 4 4 50
Trout 3000 2000 200 800 850 150 5
Human 1 1 0 0 0 1 100
Pheasant 15 12 2 2 3 5 33
yolk sac
two forms of a gene, one from each parent carried in a gamete (sperm or egg cell).
Differing forms of a gene are called ALLELES. For example , the alleles for the gene
for eye colour are blue, green ,brown etc. The phenotype is the physical appearance
results from this inherited information e.g. Someone with blue eyes has the
phenotype blue eyes. The combination of alleles that causes this phenotype is called
the genotype. Genes or alleles can be said to be DOMINANT (shows up in the
phenotype) or RECESSIVE (hidden when it is present along with the dominant gene).
Genotype is therefore represented by 2 letters (one letter for each gene)
BB has the phenotype black it is said to have a HOMOZYGOUS genotype
Homozygous is often called ‘pure breed’ or true breeding
Bb has the phenotype black but is said to have a HETEROZYGOUS genotype
bb has the phenotype white and is said to be HOMOZYGOUS recessive.
Genetic Crosses
A genetic cross is laid out as follows:
Example
A pea plant which produces round pea seed is crossed with a pea plant which produces wrinkled peas seeds. All the offspring are round.
- Which is the dominant allele of the gene?
- What is the genotype and phenotype of the parents and F1.
- What is the genotype and phenotype of the F2?
- What is the ratio of phenotype in F2?
Turn over to see this example.
The phenotype ratio when 2 heterozygous individuals cross is always 3:
The actual ratio may differ from the expected ratio since fertilisation is a random
process. An element of chance is involved.
Family Trees
A family tree can be used to show the links between all the members of a family
