Biology paper one

The Endocrine system

Hormones are chemical molecules released directly into the blood, then carried to target organs.

Hormones are produced in various glands, that make up the endocrine system. 

The pituitary gland

  • Produces many hormones that regulate body conditions.
  • These hormones act on other glands, directing them to release hormones that bring about change.


  • Produces oestrogen, which is involved in the menstrual cycle. 


  • Produce testosterone- controls puberty and sperm production in males.
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The Endocrine system PART TWO


  • Produces thyroxine- regulates the rate of metabolism, heart rate and temperature.

Adrenal gland

  • Produces adrenaline- prepares 'fight or flight' response.

The pancreas

  • Produces insulin- regulates blood glucose levels.


  • Slower action
  • Act for a long time
  • Act in a more general way
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Abiotic and biotic factors

Abiotic factors are non-living:

  • Moisture level
  • light intensity
  • Temperature
  • CO2 levels
  • Wind intensity/direction
  • Oxygen level
  • Soil PH
  • Mineral content

A change in the environment could be an increase or decrease in an abiotic factor. 

Biotic factors are living:

  • New predators
  • Competition 
  • New pathogens
  • Availability of food

A change in the environment could be the introduction of a new biotic factor. 

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Homeostasis- maintain a stable internal environment

Conditions inside your body need to be kept steady to make sure your cells are in the right conditions in order to function properly. Including conditions for enzymes, 

Maintain a stable internal environment in response to changes in the internal and external conditions.

Our bodies have loads of automatic control systems in your body that regulate your internal environment ( both hormonal and nervous communication systems)

 Three main components in automatic control systems:

  • Receptors
  • Coordination Centres (brain, spinal cord and pancreas) 
  • Effectors
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Homeostasis PART TWO

Negative feedback

Your automatic control system keeps your internal environment stable using a mechanism negative feedback. 

Receptor detects a stimulus-level TOO HIGH/TOO LOW

The CC receives and processes the information, the organises a response

Effector produces a response which counteracts the change and restores the optimum level- the level DECREASES or INFECTION 

The effectors will carry on producing responses for as long as they're stimulated by the CC.

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Meiosis is a slightly different process. It is used to create the gametes, these are the sperm or eggs, used in sexual reproduction. The offspring produced during sexual reproduction have characteristics, selected from those of the parents.

The main difference in meiosis as compared to mitosis is that the new cells have half the number of chromosomes as the diploid 'parent' cell. One chromosome comes from each homologous pair of chromosomes. So these offspring cells are haploid, not diploid.

  1. Meiosis starts with all the chromosomes lining up in their (homologous) pairs.
  2. One chromosome from each pair enters a new nucleus so that 2 daughter cells are formed.
  3. The 2 daughter cells now have half the number of chromosomes each compared to the 'parent' cell. They are haploid.
  4. The chromatids that make up each chromosome are pulled apart by fibres.
  5. Every single chromatid joins the others in another new nucleus. These are the gamete cells. These cells are haploid too.
  6. The chromatids in the gamete cells are replicated to re-create the X-shaped chromosome. The gametes are haploid.

Finally, then you end up with 4 gamete cells from each parent cell that splits up. These gamete cells, whether eggs or sperm, can then go on to fertilisation.

No gamete is ever the same as the next.

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