COMPLETE VERIFIED NOTES ON AQA SCIENCE B2 1.1-3.6

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Biology Revision Notes B2 1.1-3.6
Animal and Plant Cells:
Animal Cells - Structure and function:
Nucleus: This controls all of the activities of the cell. It also
contains instructions for making new cells or new organisms.
Cytoplasm: This is a liquid gel in which most of the chemical
reactions needed for life take place, including respiration.
Cell Membrane: This controls the passage of substances in and out of
the cell.
Mitochondria: These are found in the cytoplasm where oxygen is
used and where most of the energy is released during respiration.
Ribosomes: These are where protein synthesis takes place.
All proteins that are needed in the cell are made here.
Simple diagram of animal cell:

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Plant cells ­ Structure and Function:
Plant cells are very different to animal cells.
All plant cells have the following organelles:
Cell Walls: These are made of cellulose and strengthen the
cell, giving it support.
Many (but not all) plant cells also have these other features:
Chloroplasts: These are found in the green parts of the plant.
They are green because they contain a green pigment called
chlorophyll. They absorb light energy in order to make food by
photosynthesis.…read more

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Chemical Reactions within cells:
Cell chemistry works because each reaction is controlled by an
enzyme.
Each enzyme is a protein which controls the rate of a very specific
reaction.
It makes sure that the reaction takes place without becoming
mixed up with any other reaction.
Enzymes are found throughout cells, but particularly in the
mitochondria (and chloroplasts in plants).
Enzymes involved in different chemical processes are usually found in
different areas of the cell. For example:
Enzymes controlling respiration are found in the mitochondria.…read more

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Sometimes cells become so specialised that they only have one
function within the body.
Good examples of this include sperm cells, eggs, red blood cells
and nerve cells.…read more

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Organised cells:
Specialised cells are often grouped together to form a tissue.
Connective tissue joins bits of a person's body together.
Nervous tissue carries information around a person's body.
In plants, photosynthetic tissues make food by photosynthesis while storage
tissues store any extra food made as starch.
In larger living organisms several different tissues work together to do
particular jobs. These are called organs and examples of these include the
heart, the kidneys or the leaf.…read more

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Diffusion happens when the particles
of a gas, or any substance in solution,
spread out.
It is the net movement of particles
from an area of high concentration to
an area of lower concentration.
It takes place because of the random movement of the particles of a gas or of a
substance in solution in water.
Rates of diffusion:
If there is a large difference in concentration between two areas,
diffusion will take place quickly.…read more

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Simple sugars, such as glucose and amino acids from the breakdown of
proteins in your gut, can pass through cell membranes by diffusion.
The oxygen you need for respiration passes from the air into your lungs
and into your cells by diffusion.
Individual cells may be adapted to make diffusion easier and more rapid.
The most common adaptation is to increase the surface area of the cell
membrane over which diffusion occurs. This means that there is more
room in which diffusion can take place.…read more

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In cells, there are chemicals dissolved in water inside a partially permeable bag
of cell membrane.
Cells contain a fairly concentrated solution of salts and sugars.
Water will move from a high concentration of water particles (in a dilute
solution) to a less concentrated area of water particles (in a concentrated
solution) across the membranes of cells.
This process, (a special type of diffusion), where only water moves across a partially
permeable membrane, is essentially osmosis.…read more

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This swollen/turgid state keeps the leaves and the stems of the plant rigid and firm
meaning that for all plants it is important that the fluid surrounding the cell always
has a higher concentration of water (more water than chemicals/solutes) than the
cytoplasm of the cells. This keeps osmosis working in the right direction and to their
advantage.
Active transport: This is when plant and animal cells need to move substances such as
glucose against a concentration gradient.…read more

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