B4 revision. very useful

helpful, and explains most of the parts needed to know in the HIGHER and FOUNDATION tier of OCR gateway B biology.

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  • Created on: 08-04-12 19:34
Preview of B4 revision. very useful

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Osmosis- Transfer of water from one material to another. Usually from high concentration to low.
Leafs adaptations :
Contains chloroplasts
Flat and large to absorb the most sunlight
Network of veins to transport water and remove waste products
Thin structure to allow gasses shorter distance to the cells
It has stomata to allow carbon dioxide and oxygen to diffuse
Leaf is made up of 4 layers ( In Order ):
Upper epidermis
Palisade layer
Spongy mesophyll
Lower epidermis
The features of the Leaf:
Waxy cuticle restricts water loss from the leaf
Upper epidermis is transparent to allow sunlight through
The spongy mesophyll contains lots of air spaces connected to the stomata to ensure
the optimum exchange of gasses
The lower epidermis contains most of the stomata
Stomata allows the diffusion of gasses in and out of the leaf.
Guard cells control the size of the stomata to restrict the loss of water
Veins contain xylem and phloem to transport water and sugars through the leaf
Water in plants:
Use it to keep the leaves cool
Transport materials
Enables them to photosynthesise to produce glucose
Keeps cells firm and therefore keeping the plant ridged
In the leaf, water moves out of the cell by osmosis and into the spaces in the spongy mesophyll layer
from where it will pass out of the leaf into the atmosphere.
When there is not enough water available in the soil, stomata close to try to prevent transpiration
and the diffusion of gasses, so photosynthesis has to stop. The plant cells are short of water so they
are not strong, which causes them to wilt.
Cells that lose a lot of water and contract like a deflating balloon.
The xylem and phloem form a continuous system of tubes and roots to the leaves.
Xylem vessels carry water up from the roots and phloem tubes carry food up and down the plant.
Water evaporates from the internal leaf cells through the stomata

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Water passes by osmosis from the xylem vessels to leaf cells, which pulls the entire thread
of water in the that vessel upwards by a very small amount
Water enters the xylem from root tissue to replace water which has moved upwards.
Water enters root hair cells by osmosis to replace water which has entered the xylem
Xylem vessels are hollow tubes made from dead plant cells. The cellulose cell walls are thickened and
strengthened with a waterproof substance.…read more

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Intensive farming:
Intensive farming practices in keeping animals in carefully controlled environments, where their
temperature and movement are limited. For example, fish farms breed huge numbers of fish in
enclosed nets in the sea or lakes, and battery farms raise chickens in cages. However, this can
raise ethical dilemmas; some people find this morally unacceptable because animals have
poor quality of life.
Ways on creating organic foods:
Using animal manure or compost instead of chemical fertilisers.…read more

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Saprophytes are essential for decay.
Earthworms, woodlice, and maggots are known as Detritivores; they feed on dead organisms
and the waste produced by the living organisms. Detritivores speed up the process of decay
because they break up the waste into small particles, which have a large surface area, making it
easier for decomposers to feed on. The faeces of the Detritivores provide food for the
decomposers like bacteria and fungi.…read more


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