Biology 2a - Cells, tissues and populations

  • Created by: ryyansb
  • Created on: 30-03-15 09:46


Plant and animal cells have similarities and differences

Human/animal cells have:

  • Nucleus - contains genetic material that controls the cell
  • Cytoplasm - gel-like substance where most chemical reactions take place
  • Cell membrane - holds cell together and controls what goes in and out
  • Mitochondria - where most of the reactions for respiration take place - respiration releases energy that cells need to work
  • Ribosomes - where proteins are produced in the cell

Plant cells have all of the above plus the following:

  • Rigid cell wall - made of cellulose - supports and strengthens the cell
  • Permanent vacuole - contains cell sap - weak solution of sugar and salts
  • Chloroplasts - where photosynthesis occurs
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Cells - diagrams


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Single celled organism and diffusion

Yeast is a single celled organism

Yeast is a microorganism. A yeast cell has a nucleus, cytoplasm and a cell membrane surrounded by a cell wall

Bacteria cells have no nucleus

  • A bacteria cell has a cytoplasm and a cell membrane surrounded by a cell wall
  • Genetic material floats in the cytoplasm because bacteria cells have no nucleus


Diffusion is the spreading out of particles from an area of high concentration to an area of low concentration

Happens in solutions and gases

Cell membranes only let certain things in and out

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Specialised Cells

Palisade leaf cells are adapted to photosynthesis

  • Packed with chloroplasts for photosynthesis
  • Tall shape for high surface area for absorbing carbon dioxide
  • Thin shape so more can be packed in at the top of the leaf

Guard cells are adapted to open and close pores

  • Special kidney shape which open and closes stomata

Red blood cells are adapted to carrying oxygen

  • No nucleus so more room for oxygen
  • Concave shape so higher surface area

Sperm and egg cells are specialised for reproduction

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Cell organisation and plant structure

  • Large multicellular organisms are made up of organ systems
  • Similar cells are organised into tissues
  • Tissues are organised into organs
  • Organs are organised into organ systems

Epithelial cell  ->  Epithelial tissue  ->  Stomach  ->  Digestive System


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Limiting factors of photosynthesis


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How plants use glucose

1. For respiration

  • Plants manufacture glucose in leaves
  • Use some of the glucose for respiration
  • This releases energy - build and grow cells
  • Need to gather minerals from the soil

2. Making cell walls

  • Glucose converted to cellulose for making strong cell walls

3. Making proteins

  • Glucose is combined with nitrate ions to make amino acids

4. Stored in seeds

  • Glucose turned into lipids for storing in seeds

5. Stored in starch

  • Turned into starch and stored in roots, stems and leaves 
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Distribution of organisms

Organisms live in different places because the environment varies

Where an organism is found can be affected by:

  • Temperature
  • Availability of water
  • Availability of oxygen and carbon dioxide
  • Availability of nutrients
  • Amount of light

Use quadrats to study the distribution of small organisms

Use transects to study distribution of organisms along a line

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Collecting environmental data

When collecting environmental data you need to think about


  • Quadrats and transects are good
  • Make sure results are reproducible and repeatable
  • Take a large sample size


  • Control all variables
  • Random samples
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