synoptic essays for AQA A2 biology unit 5

a test synoptic

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  • Created on: 26-05-10 11:28
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How the structure of cells is related to its function
Cells are building blocks of life. Without cells, our body (and all living things) wouldn't be alive
or working. Cells convert things into energy, send signals, and overall keep us functioning.
Group of cells forms various systems in body. There are many different kinds of cells and
each one of them is specialized to carry out its own function. Some cells are specialized for
transporting such as xylem, phloem, root hair cells and red blood cells, they all help transport
minerals and ions. Some cells are specialized for immunity, such as white blood cells.
Transporting ions, oxygen and minerals is important for cells to survive and carry out their
functions. An example of this kind of cell is red blood cell. A major function of the red blood
cells is to carry oxygen to all the tissues from the lungs. Red blood cells contain a pigment
called haemoglobin which has high affinity for oxygen. Red blood cells have a unique
appearance. They have been described as looking like a doughnut they are thinner in the
center and thicker around the edges. They are very flexible with the ability to twist and bend
through the blood vessels. The shape of it is biconcave (and like a flattened disc). This
increases surface area over volume which allows fast diffusion rate of oxygen. Red blood cell
has no nucleus which allows more space for haemoglobin to be packed. In plants, many of
the substances needed for carrying out photosynthesis and other chemical reactions are
absorbed by the plant via root hair cells. Root hair cells absorb water from the soil. Root hair
cell has a large surface area for faster and more absorption of water, it's long in shape to
allow more water to be absorbed and transported quickly. Root hair cell have large number of
mitochondria to carry out respiration which in turn produces energy for active transport. Xylem
vessels carry water and minerals into the plant. Xylem consists of fairly long tubes with thick
walls. These tubes were originally cells which died due to build up of a substance called lignin
in their cell walls. This makes the tissue impermeable (to water) so none is lost as water is
transported via the xylem. Phloem cells transport sugar in plants these sugars are used in
various chemical reactions.
Some cells are specialized for reproduction examples of these specialized cells include egg
cell and sperm cell. Sperm cells are highly specialized to their function as they contain a
lysosome called an acrosome which contains digestive enzymes which helps them penetrate
the female egg's jelly in order to fertilize it. Sperm cells have a motile tail which helps them
for movement the tail is full of mitochondria which provide energy for movement. Sperm cells
have a streamlined shape which helps them to move faster. Egg cell is bigger than the sperm
and has a chemical around the outside to stop more sperm getting in. The egg also contains
lots of cytoplasm a liquid substance found inside of it, this cytoplasm helps it to survive.
Nerve cells send and receive signals from other neurons in the body. They are adapted to
their function as they have dendrites which receive and send impulses from one neuron to
another and they also have long axons which are wrapped in a myelin sheath. The myelin
sheath protects the axon. There are gaps between the myelin sheath called nodes of ranvier.
These increase the rate of the impulse being passed along the axon.
Our body has to fight against many bacteria. Cells which help with this are called white blood

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