1 - Key Concepts In Biology

• Cell structures found in both plant and animal cells which are Eukaryotic:


  • Nucleus: Contains DNA and controls activities of the cell
  • Cytoplasm: Site of chemical reactions such as anaerobic respiration
  • Cell membrane: Selectively permeable membrane that controls what goes in and out of the cell
  • Mitochondria: Site of aerobic respiration providing energy to the cell
  • Ribosomes: Site of protein synthesis
• Cell structures found in plant cells only:

  • Chloroplasts: Site of Photosynthesis and contains chlorophyll pigment
  • Permanent Vacuole: Stores cell sap and keeps cell turgid
  • Cell Wall: Provides structure and support
• Cell structures found in bacterial cells which are prokaryotic:


  • Smaller ribosomes
  • Cell wall made of a different substance
  • Cytoplasm
  • Chromosomal DNA - Strands of DNA free floating in the cytoplasm
  • Plasmids - Small rings of DNA
  • Flagella - Long thin tail allowing the cell to move
• Sperm cells are specialised to carry the male’s DNA to fertilise the egg cell. The adaptations are:

  ● A Streamlined head and long tail to aid swimming

  ● Many mitochondria which supply the energy to allow the cell to move

  ● The acrosome has digestive enzymes which break down the outer layers of membrane of the egg cell

  ● Haploid nucleus so it has 23 chromosomes, rather than the 46 that most other body cells have
• Egg cells are specialised to accept a single sperm cell and develop into an embryo. The adaptations are:

  • Surrounded by a special cell membrane which can only accept one sperm cell (during fertilisation) and becomes impermeable following this
  • Has Lots of mitochondria to provide an energy source for the developing embryo
  • Haploid nucleus
  • Has a nutrient rich cytoplasm so the zygote receives nutrients before the placenta forms
• Ciliated cells line airways and contain small hairs called cilia which can push molecules through airways and waft away debris.
• Red blood cells carry oxygen to cells. It has a biconcave shape and no nucleus to increase its surface area and still it through the capillaries
• Root hair cells are specialised to take up water by osmosis and minerals by active transport from the soil as they are found in the tips of roots

  ● Have a large surface area due to root hairs, meaning more water can move in

  ● Mitochondria provide energy from respiration for the active transport of mineral ions into the root hair cell
• Xylem cells are specialised to transport water and minerals up the plant from the roots to the shoots

  ● Upon formation, a chemical called lignin is deposited which causes the cells to die. They become hollow and are joined end-to-end to form a continuous tube so water and mineral ions can move through
• Total Magnification = Eyepiece magnification x objective magnification
• Magnification is how much larger the image is than the actual object
• Advantages of light microscopes over electron microscopes is that they are cheaper, form coloured images and don't require much training to use.

  However, the disadvantages are that they have a lower magnification and resolution, you cannot see ribosomes.
• Advantages of electron microscopes is that they have a higher magnification and resolution than light microscopes and you can see smaller cell structures.

  Disadvantages are that they are expensive, don't produce colour images, require training to use and can only be used on dead samples.
• Image size = Actual size x Magnification
• Amylase breaks down starch into glucose. It is produced in the salivary glands and pancreas, with an optimum pH of 7.
• Protease breaks down protein into amino acids and are found in the stomach, pancreas and small intestine.
• Lipase breaks down lipids into glycerol and fatty acids. They are produced in the pancreas and small intestine.
• Temperature effects enzyme action as increased heat energy means more kinetic energy and therefore more collisions forming more enzyme substrate complexes. Temperature higher than the optimum would denature the enzyme as the active site would irreversibly change due to broken bonds so the substrate no longer fits.
• High or Low pH effects affect enzyme action as it denatures the enzyme because the shape of the active site is changed and the substrate no longer fits.
• Increased substrate concentration increases the rate of reaction as there are more collisions and therefore more enzyme substrate complexes formed. However rate of reaction will reach a plateau.
• To test for starch, use the iodine solution test. If starch is present, the solution will change from orange to blue-black.
• To test for reducing sugars, add Benedict's solution. Mix with an equal volume of food solution and place in a hot water bath for 5 minutes. Colour change to reddish-brown indicates reducing sugar.
• To test for protein do the biuret test. Add potassium hydroxide and an equal volume of copper sulfate. If present, the solution will turn from blue to purple
• To test for lipids, do the emulsion test. Add ethanol to food and shake. Pour into water and shake again. If lipids are present they will float to the surface and form a cloudy emulsion
• Steps in calorimetry:

  1. Add cold water to copper calorimeter
  2. Record starting temperature of water
  3. Water is heated from burning food
  4. Final temperature of water is recorded.
• Energy in food (J) = Mass of water (g) x temperature change x 4.2
• Diffusion is the net movement of particles from an area of high concentration to an area of low concentration.
• Active transport is the movement of molecules from an area of low to high concentration against a concentration gradient, across a partially permeable membrane, using energy released from aerobic respiration.
• Osmosis is the movement of water particles from a high to low water concentration across a partially permeable membrane.
• Red blood cell bursts in hypotonic solution because water concentration is greater outside the cell so it moves into the cell by osmosis, and therefore the cell bursts.
• Red blood cells shrivel in a hypertonic solution because the water concentration is less outside the cell and therefore the water moves out of the cell by osmosis, causing it to shrivel.
• Phloem cells: specialised to carry the products of photosynthesis to all parts of the plants

  ● The energy these cells need to be alive is supplied by the mitochondria.