GCSE Biology (Triple) AQA

This subject is broken down into 116 topics in 9 modules:

  1. Cell Biology 12 topics
  2. Transport Systems 11 topics
  3. Organisation 16 topics
  4. Infection and Response 8 topics
  5. Bioenergetics 6 topics
  6. Homeostasis and Response 16 topics
  7. Inheritance, Variation and Evolution 18 topics
  8. Ecology 18 topics
  9. Required Practicals 11 topics
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  • 9
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  • 116
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  • 42,941
    words of revision content
  • 5+
    hours of audio lessons

This page was last modified on 9 January 2025.

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Biology (Triple)

Cell Biology

Cell Biology: Cells

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Cell Biology: Cells

1. Basics of Cells:

  • All living organisms are composed of cells.
  • Cell is considered as the basic unit of life.

2. Types of Cells:

  • There are two main types of cells: prokaryotic and eukaryotic.
  • Prokaryotic cells do not have a nucleus or membrane-bound organelles. Bacteria are typical examples.
  • Eukaryotic cells have a nucleus and membrane-bound organelles. Animals and plants are composed of eukaryotic cells.

3. Parts of a Eukaryotic Cell:

  • Key parts of a eukaryotic cell include nucleus, cytoplasm, cell membrane, mitochondria and ribosomes.
  • The nucleus controls the activities of the cell and contains genetic material.
  • The cytoplasm is a gel-like substance where most of the chemical reactions occur.
  • The cell membrane is responsible for controlling the passage of substances into and out of the cell.
  • Mitochondria are the site of aerobic respiration and where most energy is released.
  • Ribosomes are the site of protein synthesis.

4. Plant Cells and Animal Cells:

  • In addition to all the parts present in an animal cell, a plant cell also has cell wall, chloroplasts and a permanent vacuole.
  • Chloroplasts are where photosynthesis occurs.
  • The cell wall provides added strength and support to the cell.
  • Permanent vacuole contains cell sap, a weak solution of sugar and salts.

5. Specialised Cells:

  • Cells may be specialised to carry out a particular function.
  • Examples include sperm cells, nerve cells and root hair cells in plants.

6. Microscopy:

  • Light microscopes allow us to see the cells and large organelles like nuclei.
  • Electron microscopes have much higher resolution and magnification so smaller details, like ribosomes and plasmids, can be seen.

7. Cell division and Differentiation:

  • Cells divide in a series of stages called the cell cycle.
  • During the cell cycle, the genetic material is duplicated and then divided into two new cells.
  • In mature animals, cell division is mainly used for repair and replacement.
  • In plants, cells retain the ability to differentiate throughout life.
  • Differentiation is the process by which a cell changes to become specialised for its job.

Course material for Biology (Triple), module Cell Biology, topic Cell Biology: Cells

Biology (Triple)

Homeostasis and Response

Homeostasis and Response: The Eye

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Homeostasis and Response: The Eye

The Structures of the Eye

  • The eye is a complex organ with numerous structures, each with their own specific functions.
  • The retina is a layer at the back of the eyeball that contains cells sensitive to light (photoreceptor cells).
  • The cornea refracts, or bends, light into the eye.
  • The iris is the coloured part of the eye which controls how much light enters the eye by changing the size of the pupil.
  • The lens focuses light onto the retina.
  • The sclera is the white part of the eye, it is tough and protective.
  • The ciliary muscles and suspensory ligaments control the shape of the lens.

Adapting to Light Levels

  • When light levels are high, the iris makes the pupil smaller to limit the amount of light entering the eye, a process known as constriction.
  • Conversely, in low light conditions, the iris widens the pupil (dilation) to allow more light to enter the eye.
  • Accommodation is the process by which the eye changes the shape of the lens to focus light onto the retina.

Focusing on Near and Distant Objects

  • To focus on a distant object, the ciliary muscle relaxes and the suspensory ligaments are taut, making the lens go thin and less refractive.
  • To focus on a near object, the ciliary muscle contracts and the suspensory ligaments slacken, allowing the lens to become round and more refractive.

Common Problems with the Eye

  • Long-sightedness (hyperopia) occurs when the eye is unable to focus on near objects and is corrected with a convex lens.
  • Short-sightedness (myopia) occurs when the eye is unable to focus on distant objects and is corrected with a concave lens.
  • Colour blindness is a genetic disorder that affects a person's ability to see colours. It is usually a deficiency in distinguishing between red and green.

Corrective Measures for Eye Problems

  • Glasses or contact lenses can correct vision defects such as myopia or hyperopia by refracting light to compensate for the eye's inability to do so.
  • In some cases, laser eye surgery is used to change the shape of the cornea and correct the refractive errors.
  • Eye conditions such as cataracts (clouding of the lens) can be treated by replacing the faulty lens with an artificial one.

Course material for Biology (Triple), module Homeostasis and Response, topic Homeostasis and Response: The Eye

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