Cell biology

• Nucleus

  • Contains DNA coding fro a particular protein needed to build new cells.
• Cytoplasm

  Contains enzymes (biological catalysts) i.e. proteins that speed up the rate of reaction.
• Cytoplasm

  Liquid substances in which chemical reactions occur
• Cell membrane

  COntrols what enters and leaves the cell.
• Mitochondria

  Where aerobic respiration reactions occur, providing energy for the cell.
• Ribosomes

  Protein synthesis occurs
• Chloroplasts in plant cell (only)

  Photosynthesis takes place, providing food for the plant.
• Chloroplast in plant cells (only)

  Contains chlorophyll pigment (which makes it green) which harvests the light needed for phtosynthesis
• Permanent vacuole in plant cell (only)

  Contains cell sap, found within the cytoplasm and improves cell's rigidity
• Cell wall in plant cells

  Made from cellulose and provides strength to the cell
• Cell wall in bacterial cell

  made of a different compound - peptidoglycan
• Singular circular strand of DNA

  As they have No nucleus, this floats in the cytoplasm
• Plasmids

  Small rings of DNA
• What are the structures that are only found in plants cells?

  Chloroplasts, permanent vacuole and cell wall
• What is meant by the term differentiate?

  The process by which the cell changes to become specialised for its job
• What are specialised cells in animals?

  • Sperm cells : specialised to carry the males's DNA to the egg for reproduction.
  • Nerve cells : transmit electrical signals quickly from one place in the body to another.
  • Muscle Cells : to contract quickly to move bones or simply squeeze
• What are specialised cells in plants?

  • Phloem cells : to carry the products of photosynthesis to all parts of the plant
  • Root hair cells : to take up water by osmosis and mineral ions by active transport from the soil as they are found in the tips of roots
  • Xylem cells : to transport water and mineral ions up the plant from the roots to the shoots
• what are the advantages of a sperm cell

  • Streamlined head and flagella to aid swimming
  • many mitochondria which supply energy to allow the cell to move
  • Carries enzymes in the head (acrosome) which break down the outer layers of membrane of the egg cell.
• Advantages of nerve cell

  • The axon is long, enabling the impulses to be carried along long distances
  • branched connections of dendrites can form with other nerve cells.
  • have mitochondria which supply the energy to make special transmitter chemicals called neurotransmitters.
• advantages of root hair cell

  • Large surface are due to root hairs, meaning more water can move in
  • Large permanent vacuole affects the speed of movement of water from the soil to the cell
  • mitochondria to provide energy from respiration for the active transport of mineral ions
• advantages of xylem cell

  • hollow in centre so water and mineral ions can move through.
  • lignin is deposited in sprials which helps the cell withstand the pressure from the movement of water.
• advantages of phloem cell

  • Cell walls of each cell form structures called sieve plates when they break down, allowing the movement of substances from cell to cell
  • the energy the cells need is supplied by mitochondria of the companion cells.
• where are stem cells found

  • early human embryos
  • bone marrow
• embryonic stem cells

  • can differentiate into any type of cell e.g. nerve cell, skin cell and blood cell.
  • limited supply
  • ethical issues to the use of this stem cells
  • The body may reject the stem cell - can reduce the risk by using medication to supress their immune system
• adult stem cells

  • can divide by mitosis
  • can only differentiate into type of blood cells e.g. white blood cell, red blood cell and platelets.
  • replace damaged cells
• Risks of stem cells in medicine

  • Lab grown stem cells can become contaminated with a virus which can be passed on to the patient.
  • can be rejected by the patients body
  • Can develop tumors - divide quickly
• Plant stem cells

  • found in the meristem
  • persists for the plants entire life
• The process of stem cells

  1. Extract embryonic stem cells from early embryos.
  2. Grow them in a laboratory
  3. Stimulate them to differentiate into whichever type of specialised cell that we want.
  4. Give them to the patient to replace their faulty cells.
• magnification equation

  $magnification =$$image size / actual size$
• light microscope

  • Easy to use (+)
  • relatively cheap (+)
  • rely on light (-)
  • low resolution (-)
  • not good enough to study sub-cellular structures (-)
• electron microscope

  • very expensive (-)
  • hard to use (-)
  • uses electron (+)
  • better resolution (+)
  • good to study sub-cellular structures (+)
• therapeutic cloning

  • involves an embryo being produced with the same genes as the patient
  • advantage is that the patients body would not reject the stem cell as the would have the exact genetic make-up
• Diffusion

  The spreading out of particles from an area of higher concentration to an area of lower concentration
• Osmosis

  The movement of water molecules from a dilute to a concentrate across a partially permeable membrane
• Active Transport

  The movement of particles against a concentration gradient using energy transferred during respiration
• Three factors affecting diffusion

  • Concentration gradient
  • Temperature
  • Surface area
• Concentration gradient

  The grater the difference in concentration the faster the rate of diffusion. This is because more particles are randomly moving down the gradient than are moving against it.
• Temperature

  The greater the temperature, the greater the movement of particles, resulting in more collisions and therefore a faster rate of diffusion.
• Surface area of the membrane

  The greater the surface area, the more space for particles to move through, resulting in a faster rate of diffusion