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All The Topics For Science B4

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  • Created by: Georgiana
  • Created on: 16-04-11 18:10


A Leaf:

  • Contains cholorophyll which abosorbs light
  • Is broad and flat to absorb maximum sunlight
  • Has a network of veins for support& to transport water
  • Has a thin structure so gases only have a short distance to travel
  • Has stomata on the underside to allow gas exchange.

During Photosynthesis...

  • Carbon dioxide diffuses in through the stomata
  • Oxygen diffuses out through the stomata
  • Water is absorbed through the roots
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Leaves ...(cont)

Layers Of A Leaf...

  • The Upper Epidermis- Is transparent to allow sunlight through
  • The Palisade Layer- Is packed with chloroplasts to absorb maximum sunlgiht
  • The Spongy Mesophyll Layer- Has lots of air spaces to allow optimum gas exchange
  • The Lower Epidermis.
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Osmosis is the net movement of molecules by diffusion through a partially permeable membrane.

Diffusion through Plants:

1. Water is absorbed by the plant by the root hair cells which have a large surface area to take in water
2. The water then diffuses through the plant up to the leaves
3. When it reaches the leaves, water can then be lost by Transpiration.

Plants use water to:

- Keep their leaves cool
- Transport minerals
- Photosynthesise
- Keep cells firm and the plant supported.

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Osmosis... (cont)

Adaptations to reduce water loss:

  • A waxy cuticle on the surface of the leaf
  • Having majority of the stomata on the lower surface of the leaf

The stomata opens and closes to allow the Diffusion of Gases and also to Control Water Loss.

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Oosmosis In Plant Cells ...

Plant Cells Have An Inelastic Cell Wall For Support.

The cell wall...
~ Prevents cells from bursting due to excess water
~ Contributes to rigidity

  • A lack of water can cause plants to wilt
  • As water moves into plant cells by Osmosis, the pressure inside the cells increase.
  • The inelastic cell walls withstand pressure and cells become very turgid

* When all cells are fully turgid, the plant is upright
* If water is in short supply, cells lose water by Osmosis.
* Plants lose Tugor Pressure and become Flaccid

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(cont) ...

  • Plasmolysis - When Cells Lose Lots Of Water, The Inside Of The Cell Contracts.
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