AQA GCSE Science BIOLOGY 2 Unit B2.1 Cells and simple cell transport

• All living things are made up of cells.

• Know that the structures of different types of cells are related to their functions.

• Know the similarities and differences between animal cells, bacteria and plant cells.

• Know that to get into or out of cells, dissolved substances have to cross the cell membranes.

• You need to be able to use your skills, knowledge and understanding to relate the structure of different types of cells to their function.

AQA GCSE Science BIOLOGY Unit B2.1.1 Cells and cell structure

• a) Know that most human and animal cells have the following parts:

  • soft cell membrane 'wall' holding the contents together

  • a nucleus, which controls the activities of the cell and contains the genetic material - genes-DNA

  • cytoplasm, in which most of the chemical reactions take place usually via enzyme catalysts

  • a cell membrane, holds the cytoplasm together and controls the passage of substances into and out of the cell

  • mitochondria, which is where most energy is released in respiration - eg 'burning' glucose to release energy

  • ribosomes, which is where protein synthesis from amino acids occurs.

• b) Know that plant and algal cells also have a rigid cell wall made of cellulose, which strengthens the cell and therefore the plant's structure.

  • Plant cells often have:

    • chloroplasts, which absorb light energy to make food via chlorophyll in photosynthesis

    • a permanent vacuole filled with cell sap containing sugars and mineral salts.

• c) Know that a bacterial cell consists of cytoplasm and a membrane surrounded by a cell wall; the genes are not in a distinct nucleus - a sort of jumbled cluster.

  • Bacteria do not have a nucleus.

  • The genetic material ie DNA just forms a cluster in the cytoplasm.

•  d) Know that yeast is a single-celled organism.

  • Know that yeast cells have a nucleus, cytoplasm and a membrane surrounded by a cell wall.

• e) Know and understand that cells may be specialised to carry out a particular function e.g.

  • Animal cells

    • Red blood cells to carry oxygen via their haemoglobin molecules.

    • White blood cells of the immune system.

    • Gamete cells ie egg cells and sperm cells are the sexual reproduction cells.

  • Plant cells

    • Palisade leaf cell structure is adapted to support the sites of photosynthesis.

    • Guard cells can open and close the pores (stomata) in leaves - they must allow oxygen and carbon dioxide to pass in and out.

AQA GCSE Science BIOLOGY Unit B2.1.2 Dissolved substances

• a) Know that dissolved substances can move into and out of cells by diffusion through the cell membrane.

• b) Know that diffusion is the spreading of the particles of a gas, or of any substance in solution, resulting in a net movement from a region where they are of a higher concentration to a region with a lower concentration.

  • Diffusion occurs spontaneously due to the random movement of fluid particles - all gas, liquid or dissolved particles have kinetic energy of movement.

  • Know that the greater the difference in concentration, the faster the rate of diffusion, due to the steeper concentration gradient.

  • Only relatively small molecules can diffuse through cell membranes eg amino acids but not proteins, sugars like glucose but not large carbohydrate molecules like starch.

• c) Know that oxygen required for respiration passes through cell membranes by diffusion.

  • Diffusion occurs in all mixtures of gases, liquids or solutions.

  • Anything dissolved in a solution can spread or diffuse if there is a difference in concentration ie a net transfer of the substance from one place to another eg through a cell membrane.

• Your practical work to develop your skills and understanding may have included the following:

  • observation of cells under a microscope, eg sprouting mung beans to show root hair cells

  • computer simulations to model the relative size of different cells, organelles and molecules

  • computer simulations to model the process of diffusion

  • making model cells

  • diffusion of ammonium hydroxide in a glass tube using litmus as the indicator

  • investigate how temperature affects the rate of diffusion of glucose through Visking tubing.