Additional Biology Revision Notes

These notes summarise unit 2 biology, including higher tier.

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Additional Biology
Animal and plant cells
Most animal cells contain a:
o Nucleus
o Cytoplasm
o Cell membrane
o Mitochondria
o Ribosomes
Plant cells contain all the structures seen in animal cells as well as:
o A cell wall
o Chloroplasts
o A permanent vacuole
The tables below show the function of animal and plant cells.
Part (Animal) Function
Nucleus Controls the activities of the cells, and contains the genetic instructions needed
to make new cells or organisms.
Cytoplasm A liquid gel in which most of the chemical reactions needed for life take place,
like respiration.
Cell Membrane Controls the passage of substances in and out of the cell.
Mitochondria Structures in the cytoplasm where oxygen is used and most of the energy is
released during respiration.
Ribosomes Where protein synthesis takes place.
Part (Plant) Function
Cell wall Made of cellulose - strengthens the cell and gives it support.
Chloroplasts These are found in all the green parts of the plant. They are green because they
contain the green substance chlorophyll which gives the plant its colour. They
absorb light energy to make food by photosynthesis.
A permanent Is a space in the cytoplasm filled with sap, which is important for keeping the cells
vacuole rigid to support the plant.
Enzymes control the chemical reactions inside cells.
Specialised cells
Cells may be specialised to carry out a particular function.
Examples of specialised cells are:
o Fat cells
o Cone cells
o Root hair cells
o Sperm Cells
Movement of substances in and out of cells

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Dissolved substances move in and out of cells by diffusion, osmosis and active transport.
Diffusion is the passive net movement of particles from an area where they are at a high
concentration to an area where they are at a lower concentration.
Osmosis is a special case of diffusion.
Osmosis is the passive diffusion of water from a high water concentration to a low water
concentration through a partially permeable membrane.…read more

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Radiation from the Sun is the main source of energy for all living things. The Sun's energy is
captured and used by plants during photosynthesis.
The mass of living material at each stage of a food chain is less than at the previous stage.
The biomass at each stage can be drawn to scale and shown as a pyramid of biomass.
Energy losses
The amount of biomass and energy gets less at each successive stage in a food chain.…read more

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Biomass and energy are lost at each stage of a food chain. The efficiency of food production
can be improved by reducing the number of stages in our food chains. It would be most
efficient if we all just ate plants.
If you stop animals moving about and keep them warm, they lose a lot less energy. This
makes food production much more efficient. This is known as battery farming.
Living organisms remove materials from the environment as they grow.…read more

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The constant cycling of carbon in nature is known as the carbon cycle.
Carbon dioxide is removed from the atmosphere by photosynthesis. It is returned to the
atmosphere through respiration and combustion.
The energy originally captured by green plants is eventually transferred into consumers,
decomposers or as heat into the environment.
Enzyme structure
Catalysts increase the rate of chemical reactions. Enzymes are biological catalysts.
Enzymes are protein molecules made up of long chains of amino acids.…read more

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Aerobic respiration involves chemical reaction which use oxygen and sugar and release
energy. The reaction is summed up as:
Glucose + oxygen > carbon dioxide + water [+ energy]
Most of the reactions in aerobic respiration take place inside the mitochondria.
Enzymes in digestion
Enzymes catalyse the breakdown of large food molecules during digestion.
Digestive enzymes are produced inside cells but they work outside of cells in the gut.…read more

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The enzymes made in the pancreas and the small intestine work best in alkaline conditions.
Bile produced by the liver neutralises acid and emulsifies fats.
Making use of enzymes
Some microorganisms produce enzymes which pass out of the cells and can be used in
different ways.
Biological detergents may contain proteases and lipases.
Proteases, carbohydrases and isomerase are all used in the food industry.
Controlling internal conditions
The internal conditions of your body have to be controlled to maintain a constant internal
environment.…read more

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The pancreas produces the hormone insulin, which allows glucose to move from the blood
into the cells.
In diabetes, the blood glucose may rise to fatally high levels because the pancreas does not
secrete enough insulin. It can be treated by injections of insulin before meals.
Cell division and growth
In body cells, chromosomes are found in pairs.
o Mitosis is where body cells divide to produce more identical cells for growth, repair,
replacement or in some cases asexual reproduction.…read more

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Embryonic stem cells (from human embryos) and adult stem cells (from adult bone marrow)
can be made to differentiate into many different types of cells.
Using stem cells
o Using stem cells, scientists may be able to culture new types of cells, like nerve cells
for people who have been paralysed. If new nerves grown from stem cells could be
used to reconnect the spinal nerves, people who have been paralysed could walk
again.…read more

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Meiosis is a special form of cell division where the chromosome number is reduced
by half.
o When a cell divides to form gametes, the first stage is very similar to mitosis.
o The chromosomes are copied so there are four sets of chromosomes. The cell then
divides twice in quick succession to form four gametes, each with a single set of
chromosomes.…read more


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