Prevent synthesis of enzymes needed for DNA replication or radiation can damage the DNA.
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Why are breaks needed between cancer treatments?
So the patient can recover from one treatment and produce new healthy cells which were killed.
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What is cell differentiation?
When a cell becomes specialised to preform certain functions.
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How is haemoglobin specialised?
4 'haem' groups on each polypeptide chain so it can carry 4 oxygen molecules.
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How is a palisade mesophyll cell specialised?
Contains lots of chloroplasts for photosyntesis and have very thin walls for carbon dioxide to easily enter.
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What is a tissue?
A group of similar cells that all preform the same function.
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Examples of tissues
Epitheliums (squamous epithilium in the lungs) phloem tissues, xylem tissues.
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What is connective tissue?
A few specialised cells in a non-cellular matrix eg bones, cartliage and blood.
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What is an organ?
A structure that is made of several different types of tissue. Each tissue preforms its own function which is essential for the overall functioning of the organ.
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Examples of organs
The heart, arteries, veins, lungs, leaves.
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Bodily systems
Organs are organised into systems, each system has a particular function eg circulatory system, respiratory system, digestive system, the shoot system in plants.
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Surface area to voluma ratios
Smaller animals have larger surface area to volume ratios then larger animals. So small animals lose heat more easily.
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3 adaptions needed for efficient gas exchange
-Large surface area -Thin for a short diffusion distance -Steep concentration gradient
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Structure of fish gills
Lots of gill filaments each of which has many gill lamella which provide a large surface area.
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Lamellae
Covered with lots of capillaries and a thin surface to shorten the diffusion pathway.
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Gas exchange in a fish
Water containing oxygen enters the fish through its mouth and passes out through the gills.
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What is counter current?
In a fish the water flows in the opposite direction to the blood in the capillaries to maintain a concentration gradient.
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Gas exchange in an insect
Air-filled pipes called tracheae which air moves into through pores in the surface called spiracles. Tracheoles branch off the tracheae to carry air directly to the cells.
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Gas exchange in plants
Gasses move in and out the leaf by the stomata which can be closed by guard cells if too much water is lost. The spongy mesophyl provides a large surface area.
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