SUMMARY OF UNIT 2 – MULTICELLULAR ORGANISMS
Key Area 1 – Sexual and asexual reproduction and their importance for
survival of species.
Reproduction is the way to make new members of a species.
1) Sexual Reproduction in animals
Sexual reproduction increases variety in offspring because there is a mix of
genes from mother and father.
In animals the female sex cell is the egg which are produced in the ovary. The
male sex cell is sperm which are produced in the testes.
Female reproductive system:
Male reproductive system:
Fertilisation is when the nucleus of a sperm and egg join together. The new cell
is called a zygote. This happens in the oviduct (egg tube). Watch this video of
fertilisation at http://www.bbc.co.uk/learningzone/clips/humanfertilisation/1849.html
Once the zygote reaches the uterus it sinks (implants) into the lining of the
uterus which is thick and cushioned with blood.
The growing baby is protected in the
uterus by an amniotic sac filled with
amniotic fluid which acts as a cushion.
The growing baby gets all the oxygen
and nutrients it needs from the
mother’s blood through the placenta
and umbilical cord. The baby can also
get rid of carbon dioxide and waste
by going the oppposite way.
Unfortunatley it’s not just good stuff that passes through the placenta to the
baby. Alcohol and nicotine can also pass across.
Watch the video of a baby develop at
http://www.bbc.co.uk/bitesize/standard/biology/animal_survival/reproduction_
and_responding_to_the_environment/revision/3/
Sperm need something to swim in. Mammals don’t live in water, so the sperm
must be placed inside the female so there is liquid for them to move. This is
called internal fertilisation because it happens inside the body.
Fish release their sperm and eggs into the water – this is called external
fertilisation. This is less successful than internal because of other hungry fish
that might eat the eggs etc.
2) Sexual reproduction in plants
In plants, the flowers handle
reproduction. All flowers have
both male and female parts. The
male sex cell is inside pollen
produced by the anther. The
female sex cell is inside the ovule
produced by the ovary.
Pollination is the transfer of pollen
from an anther to a stigma. Once
pollen has landed on a stigma it grows a pollen tube down into the ovary so that
fertilisation can take place.
Once the ovule has been fertilised it turns into a seed and the surrounding
ovary develops into a fruit.
For the seed to form a new plant it has to be dispersed. There are three ways
to do this: wind (like in dandelions), animal internal (animals eat fruit) and
animal external (seed sticks to animal’s coat).
Key Area 2 – Propagating and Growing Plants
Structure of a seed:
Grows into the plants roots
Grows into the plants shoot
Provides energy for growth
Protects the seed
The growth of a seed into a plant is called germination. Germination needs
warmth, oxygen and water (WOW!). Once the plant is growing, it needs lots of
light and carbon dioxide.
Planting seeds is called sowing.
To make plants grow better, they can
be grown in polytunnels. This keeps
them warm. The farmer might also
want to hang lights.
Asexual reproduction is when new
plants are produced by a single parent .The new plants formed by this method
are genetically identical to the parent. This decreases variety.
Ways to asexually reproduce include by tubers (potatoes), runners (Spider plant
and strawberries) and bulbs (onions and daffodils). Plants can also reproduce
asexually by with the help of man (cuttings and grafting).
Fertilsers contain three key elements required by the plant; Nitrogen (for
leaves), Phosphorous (for roots) and Potassium ( for fruit and flowers) (NPK).
Rooting powder can also be used to improve the growth of roots.
You might want to watch this video at
http://www.bbc.co.uk/bitesize/standard/biology/world_of_plants/growing_plan
ts/video/ to revise growing plants.
Key Area 3 – Commercial Uses of Plants
Humans can use plants as: food (e.g potatoes, wheat & rice), raw materials (e.g
pine trees used for paper, furniture, fuel for
burning) and medicines (e.g morphine from
poppies).
Humans can change crops to produce
medicines – this is called pharming. Medicines
produced this way are easier and cheaper to
produce than is currently possible.
Medically important products that could be
produced in plants include antibodies,
vaccines and hormones.
Key Area 4 – Genetic information
Organisms are members of the same species if they can reproduce and make
fertile offspring. E.g. horses and donkeys are not the same species because
when they mate they produce mules which are infertile.
Species have lots of variation, which means
how different they are. Humans differ in
many ways including gender, eye colour, hair
colour and whether they can roll their
tongue.
Variation is controlled by genes. We receive
two genes for every characteristic (one
from our mother and one from our father).
All these peppers are the same
species, but they all have lots of
variation.
Genes have many forms. For example, in eye colour there are blue, green and
brown genes. Some genes are more ‘powerful’ (dominant genes) than others and
can overpower ‘weaker’ genes (recessive genes). If someone has a dominant gene
then it will be the only one that shows. Dominant genes get a capital letter for a
symbol and recessive genes get the same letter but in lower case.
For example, brown eyes genes are dominant to green eyes. The brown eye gene
will therefore get the symbol B and the green eye genes will get the symbol b.
A person’s actual eye colour will depend on which two genes are inherited.
Look – the
dominant
gene is
overpowering
!
Gene from mother
B
B
b
Gene from father
B
b
b
Colour of eyes
brown
brown
green
When an individual has two of the same genes (like BB or bb) they are called
truebreeding.
Key Area 5 – Growth and Development
Animals need food for energy, protection and building material. There are five
main food groups for humans:
Carbohydrates – Needed for energy (e.g bread)
Protein – Needed for growth & repair (e.g. meat)
Fat – Needed for energy (e.g. oil)
Minerals & Vitamins – Needed for protection from disease (e.g calcium, Vitamin
C)
If you don’t have enough of these food groups in your diet you will get a
deficiency. For example, someone with scurvy has no vitamin C. Vitamin D is
needed for growth of health bones. Iron is a mineral needed for bones too.
Chemicals can have an effect on baby growth while in the uterus. Lead (found in
old drinks pipes) can affect development. Thalidomide causes limb deformities.
Alcohol can lead to slower growth and poor mental development.
Key Area 6 – Biological actions
Parts of the brain:
A reflex is an automatic response by the
body to protect it from danger. It is
unconscious and rapid and works by bypassing
the brain. A sneeze is a type of reflex.
Keeping the bodies internal environment (e.g.
temperature or blood sugar) within ideal
limits is called homeostasis.
Temperature
If the body temperature drops it can lead to hypothermia which can be fatal.
A drop in temperature in the blood is detected by receptors in the skin which
send nerve impulses to increase the body’s temperature. These changes are:
shivering, body hairs standing on end and the blood vessels get narrower
If body temeprature increases (e.g fever) it is even more dangerous than a
decrease in body temeprature. Again this is detected by the body which brings
about changes to correct it. These changes are: increased sweating and the
blood vessels get wider.
Blood Glucose
Control of blood glucose (sugar) is carried out by the hormone insulin which is
released by the pancreas, not by nerves.
Insulin travels round the body in the blood. Diabetes
is a condition where patients don’t produce enough
insulin to control their blood glucose and can be fatal.
It is caused by either a failure of the pancreas to
release insulin (Type 1) or failure of the liver to
respond to insulin (Type 2).