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Unit 2

12.1 Animal and plant cells

All living things are made up of cells. The structures of different types of cells are related to their

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Unit 2

The chemical reactions inside cells are controlled by enzymes

Enzyme for respiration are in mitochondria
Enzyme for photosynthesis are in chloroplasts
Enzymes for protein synthesis are on the ribosomes

Some cells are specialised to carry out a particular function.

Root hair cells have a tiny hair like structure…

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Unit 2

12.2 Movement into and out of cells

To get into and out of cells, dissolved substances have to cross the cell membranes

Dissolved substances can move into and out of cells by diffusion and osmosis

Diffusion is the net movement of particles from an area of high concentration…

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Unit 2

Osmosis is the movement of water across a partially permeable membrane from a region of
high water concentration to a region of lower water concentration.

The effect of osmosis is to gradually dilute the solution. This is what happens at root hair cells where
water moves from the…

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Unit 2

Osmosis in plant cells

In hypotonic solution-distilled water

Plant cell in hypertonic solution

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Unit 2

12.3 Photosynthesis

Green plants use light energy to make their own food. They obtain the raw materials they need to
make this food from the air and soil.

Four things are needed for photosynthesis to occur-
- Light from the sun -
Carbon dioxide diffused from the air…

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Unit 2

Plants use glucose for 6 different reasons-

For respiration-this releases energy that enables them to convert the rest of the glucose into
various other useful substances which they use to build new cells and grow.
Making fruits- glucose, along with another sugar fructose, is turned into sucrose for…

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Light intensity-as the light intensity s increased so does the rate of photosynthesis (only to a
certain point) this means light intensity is a limiting rate of photosynthesis.

Rise in light intensity only has effect up to some point and then begins to level out. This
means light…

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Unit 2

12.4 Energy flow in ecosystems

Food chains

Radiation from the sun is the source of energy from most communities of living organisms. In green
plants, photosynthesis captures a small fraction of the solar energy which reaches them. The energy
is stored in substances which make up the cells…

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Unit 2

In the pyramid above, the fox gets the last tiny bit of energy and biomass that is left. Only a fraction
of the suns energy is captured by the producers. Much of the biomass remains in the root system
and so does not get eaten. Rabbits run, mate,…


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