B4 It's A Green World

Module B4 'It's a green world' revision cards.

OCR Gateway GCSE Biology Higher Tier

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Leaf Structure

Carbon Dioxide + Water --> Glucose + Oxygen

Features of Leaves for Efficient Photosynthesis.

- large surface area exposed to light

- Thin: CO2 and water vapour have short distance to travel to reach the cells where it's needed.

- Contain lots of chlorophyll  (pigment that absorbs light energy for photosynthesis)

- Network of veins that deliever water and other nutrients to all of the leaf

- Upper Epidermis is transparent, so light can pass through easily to the palisade layer.

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Leaf Structure

Leaf Structure  (http://www.hcs.ohio-state.edu/hcs300/gif/tsleaf.gif)

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Diffusion in Leaves

DIFFUSION IS THE NET MOVEMENT OF PARTICLES FROM AN AREA OF HIGH CONCENTRATION TO AN AREA OF LOW CONCENTRATION

- Diffusion of gas within leaves is vital for photosyntheisis. 

- CO2 diffuses into the leaves.

- Oxygen and Water Vapour diffuse out the leaf

- O2 is made as a waste product of photosynthesis.

- Some O2 is is used in respiration, the rest diffuses out of the leaf, via the stomata

- At night, photosynthesis does NOT take place. Lots of CO2 is made in respiration, lots of O2 is used up. At night, diffusion is mainly CO2 diffusing out and O2 diffusing in.

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Osmosis

Osmosis is the movement of water molecules across a partially permeable membrane from an area of high concentration to an area of low concentration.

-Osmosis is basically diffusion of water.

- 'Partially Permeable Membrane' is a membrane that only allows certain substabnces to diffuse through it. (eg./ water can pass through, but not glucose)

-There is a net movement of water molecules during osmosis.

- When plants have plenty of water, the cells take water in by osmosis. The cells become swollen- or turgid.

 

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