Cell Biology (B1)

• Eukaryotes and Prokaryotes

  • Eukaryotic cells contain their genetic material (DNA) in a nucleus
  • In Prokaryotic cells, the DNA is not enclosed in a nucleus
  • Prokaryotic cells are much smaller than eukaryotic cells
  • Prokaryotic cells' genetic material consists of a single loop of DNA
  • Bacteria may have small rings of DNA called Plasmids
• Similarities in Plant and Animal Cells

  • Nucleus = contains genetic material that controls the activities of the cell
  • Cytoplasm = where most of chemical reactions take place
  • Cell membrane = holds cell together and control what goes in and out
  • Mitochondria = where aerobic respiration takes place - transfers energy to cell
  • Ribosomes = where protein synthesis takes place
• Plant Cells

  • Cell wall = made of cellulose, strengthens the cell
  • Vacuole = contains cell sap
  • Chloroplasts = where photosynthesis takes place, contains a green substance called chlorophyll, which absorbs light for photosynthesis
• Sizes of Cells

  • 1cm (centimetre) = 1 x 10⁻²m
  • 1mm (millimetre) = 1 x 10⁻³m
  • 1µm (micrometre) = 1 x 10⁻⁶m
  • 1nm (nanometre) = 1 x 10⁻⁹m
• Order of Magnitude

  • Things that are the same size would be the same order of magnitude
  • 1 order of magnitude = 10x
  • Every order of magnitude is 10x greater than the one before (eg. 2 orders of magnitude = 100x, 3 orders of magnitude = 1000x)

  Example: A fox is 40cm long, a tick living on the fox is 0.4cm long. How many orders of magnitude bigger is the fox?


  40/0.4 = 100x so its 2 orders of magnitude
• Animal Cell Specialisation

  • Most animal cells are specialised
  • They have adaptations that help them carry out their specific function
  • When cells become specialised it's called differentiation
• Sperm Cell (specialised cell)

  • job of a sperm cell is to join with a egg cell (fertilisation)
  • during fertilisation, the genetic material of the egg and sperm cell combine
  • contain genetic material in the nucleus (only half the genetic material of a normal adult cell)
  • have long tail, which allows them to swim to egg cell (they are streamlined to make this easier)
  • contain many mitochondria to provide energy for swimming
  • contain enzymes which allow them to digest through the egg cell
• Nerve Cell (specialised cell)

  • job of a nerve cell is to send electrical impulses around the body
  • has a long axon that carries the electrical impulses from one part of the body to another
  • axon is covered with myelin which insulates the axon and speeds up the transmission of nerve impulses
  • end of the axon has synapses, which are junctions that allow the impulse to pass from one nerve cell to another
  • cell body of the nerve cell has dendrites that increase the surface area so other nerve cells can connect more easily
• Muscle Cell (specialised cell)

  • muscle cells can contract (get shorter)
  • they contain protein fibres which can change their length
  • when a muscle cell contracts, the protein fibres shorten, decreasing the length of the cell
  • contain many mitochondria to provide energy for muscle contraction
  • muscle cells work together to form muscle tissue
• Plant Cell Specialisation

  • Most plant cells are specialised
  • They have special adaptations, which help them carry out their specific function
  • When cells become specialised, it's called differentiation
• Root Hair Cell (specialised cell)

  • root is covered with hairs that increase its surface area, so it can absorb water and dissolved minerals more effectively
  • root hair increases the surface area of the root
  • do not contain chloroplasts as they are underground and do not require them for photosynthesis
• Xylem Cells (specialised cell)

  • found in plant stem
  • form long tubes, that carry water and minerals from the roots to the leaves
  • have thick walls containing lignin (chemical), which provides support to the plant
  • because cell walls are sealed with lignin, it causes the xylem cells to die
  • end walls between the cells have broken down, so cells can form a long tube for water and minerals to flow easily
  • xylem cells have no organelles to allow water and minerals to flow easily

  A) thick walls containing lignin

  B) remains of end walls

  C) water
• Phloem Cells (specialised cell)

  • phloem tubes carry dissolved sugars up and down the plant
  • phloem consists of 2 different types of cells (phloem vessel cell & companion cell)
  • phloem vessel cells have no nucleus and limited cytoplasm
  • end walls of vessel cells have pores called sieve plates, which allow dissolved sugars to move through the inside of the cell
  • each vessel cell has a companion cell connected by pores
  • mitochondria in the companion cell provide energy to the phloem vessel cell

  A) phloem vessel cell

  B) sieve plates

  C) pore

  D) companion cell

  
• Microscopes (Required Practical)

  1. Place slide onto the stage, use clips to hold the slide in place
  2. Select lowest power objective lens (usually 4x)
  3. Position the objective lens so it almost touches the slide (slowly turn coarse focussing dial)
  4. Look through the eyepiece
  5. Slowly turn the coarse focusing dial, until the cells come into focus
  6. Then use the fine focusing dial to bring the cells into a clear focus
  7. To calculate total magnification, multiply the magnification of the eyepiece lens by the magnification of the objective lens (10x x 4x = 40x). Then select a higher power objective lens (10x)
• Microscopes (Required Practical)

  1. Place slide onto the stage, use the clips to hold slide in place
  2. Select lowest power objective lens (usually 4x)
  3. Position objective lens so it almost touches slide (slowly turn coarse focussing dial)
  4. Look through eyepiece
  5. Slowly turn coarse focusing dial (increases distance between objective lens and slide), until cells come into focus
  6. Use fine focusing dial to bring cells into a clear focus
  7. To calculate total magnification, multiply magnification of eyepiece lens by magnification of objective lens (10x x 4x = 40x). Then select a higher power objective lens
• What is osmosis?

  The diffusion of water through a membrane
• What is the direction of water movement in osmosis?

  From dilute solution to concentrated solution
• What type of membrane allows osmosis to occur?

  Partially permeable membrane
• What happens to water in a dilute sugar solution?

  It has a high concentration of water
• What happens to water in a concentrated sugar solution?

  It has a low concentration of water
• How does osmosis affect an animal cell placed in pure water?

  The cell expands and may burst
• What is the effect of osmosis on an animal cell in a concentrated solution?

  Water moves out, causing the cell to shrink
• What happens to a plant cell placed in pure water?

  The cell becomes turgid and swollen
• Why doesn't a plant cell burst when it becomes turgid?

  The cell wall prevents bursting
• What happens to a plant cell in a concentrated solution?

  Water moves out, causing the cell to shrink
• What term describes a plant cell that has lost water and shrunk?

  Flaccid
• What are the effects of osmosis on animal and plant cells?

  • Animal cells in water: expand and may burst
  • Animal cells in concentrated solution: shrink
  • Plant cells in water: become turgid and swollen
  • Plant cells in concentrated solution: become flaccid
• Where can you find questions on osmosis?

  In the vision workbook