Biology Paper 2: Topic 5

  • Created by: Beez123
  • Created on: 22-02-19 12:40


Def: The regulation of the internal conditions of a cell or organism to maintain optimum conditions for cells to function in response to internal and external changes.

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The Eye (Focusing/Light)

Light rays are bent as they go through the eye. The light rays are focused on the most sensitive part of the retina. The following explains how the eye focuses on an object:

  • Light rays bounce off an object
  • The light rays are bent as they go throught the cornea and lens
  • An upside-down picture/ image forms on the retina
  • The optic nerve carries an electrical impulse to the brain.
  • In the brain, the picture is turned up the right way

Bright Light --- Retina         ---            CNS            ---                 Iris --- Small Pupils

                                    OPTIC NERVE        MOTOR NEURONE                 

Dim Light --- Retina         ---               CNS            ---                 Iris --- Big Pupils

                                    OPTIC NERVE        MOTOR NEURONE                 

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The Eye (Accommodation)

Def: The ability to focus on near and far objects

When we look at an object that is near, the light rays need to be bent more. This means that the cilary muscles will contract to make the suspensory ligaments slack. The lens is squashed fat. When we look at an object far away the light rays don't need to bend as much so the cilary muscles relax and pull on the suspensory muscles to make them tight. This pulls the lens thin.

  • Myopia-Short sighted
  • When light rays meet before the retina
  • corrective lens make the light rays bend less (concave lens)
  • Hyperopia- Long sighted
  • When light rays don't bend
  • Convex lens
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The Nervous System Questions

Describe the difference between the function of a receptor and the function of an effector.

A receptor will recieve a stimulus from the environment- an eye is an example of a receptor. It will then send an electrical impulse through the sensory neurone to the C.N.S. The effector will recieve this impulse and initiate an effect- An example of this is the muscles.

What is a synapse?

A Synapse is where two nerves meet. When an electrical impulse reaches a synapse, a neurotransmitter is released then diffuses across the gap.

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Responding to the Cold

When the body is too cold, the blood vessels constrict so that the blood enters a shunt cell. THis is called vasoconstriction. This is brought about by sphincter muscles in the walls of the arterioles. Goosebumps are formed meaning the muscles contract so that the hairs stand on end. As air is a good insulator, the hair traps the air and keeps the body warm. Shivering also occurs meaning the muscles contract and relax rapidly generating heat for the body.

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Responding to Heat

If the body is too hot...

The blood vessels dilate so that the blood flows through the surface vessels (closer to the skin) meaning heat is radiated out of the body, keepng the body cool. Hair muscles relax so that the hair lies flat meaning that air can move and keep the body cool rather than acting as an insulator. The heat causes sweat to evaporate from the body.

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Endocrine System

Pituitary Gland-   Growth hormone- Most Cells

Thyroid Gland-    Thyroxine-            Most Cells

Adrenal Gland-    Adrenaline-           Heart

Pancreas-            Insulin-                  Liver

Ovaries (female)- Oestrogen-           Uterus

Testes (male)-      Testerone-            Muscles

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Blood Glucose

The pancreas controls blood glucose concentration

When there is too much glucose in the blood, Insulin is produced in the pancreas which causes glucose to move to muscle/ liver cells it into glycogen.

When there is too little glucose in the blood, Glucagon converts the glycogen to glucose.

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Puberty and the Menstrual Cycle

  • An egg is released from the ovary every 28 days.
  • Luteinising hormone will stimulate the release of an egg.
  • Progesterone and oestrogen maintain the uterus lining.
  • Follicle stimulating hormone caluses the the egg to mature in the ovaries and stimulates ovaries to produce oestrogen.
  • oestrogen stimulates the release of luteinising hormone.
  • The contraceptive implant releases progesterone which stops the release of eggs.


  • The mother is first given FSH and LH which stimulates several eggs to mature at the same time.
  • These eggs are then colected and fertilized by the sperm from the father.
  • In a laboratory, the eggs develop into embryos which are re-inserted into the womb for the mother to carry.

The success rate is low with only 25% effectiveness and it is very expensive.

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The Kidney

  • Excretes waste e.g urea
  • maintains water balance

Formation of Urea

  • Eat proteins which becomes amino-acids
  • Cannot store amino-acids as they contain toxic nitrogen
  • The excretion of amino-acids happens in the liver- deamination
  • the amino-acids will become a sugar and ammonia
  • The ammonia is urea

Isotonic Solution- no overall movement of water

Water lost from the body

  • sweat
  • urine/ faeces
  • breathing
  • kidney- osmoregulation- controlling water balance
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If the water content is too low, the plasma will be concentrated which will trigger the pituitary gland to produce ADH. ADH is then transported in the blood to the kidney where the collecting tubule becomes more permeable to water. The water is then reabsorbed back into the blood whilst the kidney will produce a small volume of urine.

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Dialysis/ Transplant


  • No problem with tissue matching
  • Machines available
  • Always have to watch diet
  • Twice a week a life- implications for work and family life
  • Expensive long term


  • Normal lifestyle, eat and drink what you like
  • Low cost
  • Need a donor, often not available
  • Need tissue match
  • surgery every 10 years
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Plant Hormones


As the light is only exposed to one area of the shoot, the auxin will collect on the dark side and cause the cells to elongate meaning the shoot will bend towards the light.

A tropism is growth by plants in response to a stimulus. Tropisms are positive when the plant, or part of the plant, grows towards a stimulus. They are negative when the plant, or part of the plant, grows away from a stimulus.

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