Animal & Plant Cells (AQA GCSE Biology): Revision Note

Animal cells

• Eukaryotic cells have sub-cellular structures, called organelles, each carrying out a particular function

• Organelles are sub-cellular compartments where specific processes take place

• The main sub-cellular structures in animal cells are:

  • the nucleus

  • cell membranes

  • mitochondria

  • ribosomes

  • cytoplasm

Use this image

Cell structures and functions

• Nucleus:

  • Contains the genetic material (DNA) which controls the activities of the cell

• Cytoplasm:

  • A gel-like substance composed of water and dissolved solutes

  • Supports internal cell structures

  • Site of many chemical reactions, including anaerobic respiration

• Cell membrane:

  • Holds the cell together, separating the inside of the cell from the outside

  • Controls which substances can enter and leave the cell

• Ribosomes:

  • Found in the cytoplasm

  • Site of protein synthesis

• Mitochondria:

  • Site of the reactions of aerobic respiration, where energy is released for cellular processes

  • Cells with high rates of metabolism (carrying out many different cell reactions) have significantly higher numbers of mitochondria than cells with fewer reactions taking place

Estimating size and area

• Estimations can be used to judge the relative size or area of sub-cellular structures in microscopy images of cells

• Estimation is useful when an exact measurement cannot easily be made, for example, because a structure has an irregular shape

  • You could estimate that a nucleus is about one-third of the width of a cell, or that a vacuole occupies about half of a plant cell’s area

Plant cells

• In addition to the sub-cellular parts found in animal cells, plant cells have:

  • a cell wall made of cellulose which strengthens the cell (algal cells also have this structural feature)

  • a permanent vacuole filled with cell sap

• Plant cells found in the leaf and stem may also contain chloroplasts

Use this image

 Plant cell structure and function

• Cell wall:

  • Made of cellulose (a polymer of glucose)

  • Gives the cell extra support, defining its shape

• Cell membrane:

  • Holds the cell together, separating the inside of the cell from the outside

  • Controls which substances can enter and leave the cell

• Chloroplasts:

  • Contains green chlorophyll pigments (to absorb light energy) and the enzymes needed for photosynthesis

• Permanent vacuole:

  • Contains cell sap

    • a solution of sugars and salts dissolved in water

  • Used for storage of certain materials

  • Also helps support the shape of the cell