Biology P1 - B1

• Total magnification = magnification of objective lens x magnification of eyepiece lens
• Resolving power - the shortest distance between two points that can be seen as separate points
• Magnification - The number of times larger than real life the image appears
• Animal cells only differentiate at an early stage.

  Plant cells can differentiate throughout life.
• Inside the nucleus, there are chromosomes which are long strands of DNA molecules.
• A gene is a small section of DNA that codes for a specific protein.
• A stem cell is an undifferentiated cell which can divide to become other types of cell.
• Stem cells from human embryos can be cloned (copied) and made to differentiate into most different types of human cells.
• Stem cells from adult bone marrow can form many types of cells including blood cells.
• In therapeutic cloning an embryo is produced with the same genes as the patient.
• Why do cells divide by mitosis?

  -Growth

  -Repair of damaged cells/ tissue
• Where does mitosis happen?

  -Every cell except gametes

  -More often in tissue that is growing or damaged
• Treatment with stem cells may be able to help medical conditions.

  Diabetes – stem cells could differentiate into cells of the pancreas

  Paralysis – stem cells could differentiate into nerve cells
• Meristem tissue in plant shoot tips can differentiate into any type of plant cell, throughout the life of the plant.
• What are the factors that affect the rate of diffusion?

  1. The difference in concentrations (concentration gradient)
  2. Temperature
  3. Surface area of the membrane.
• Diffusion is the net movement of particles from an area of high concentration to an area of low concentration.
• What can meristems do/be used for? Give two examples.

  -Rare species can be cloned (copied) to protect from extinction.

  -Crop plants with special features such as disease resistance can be cloned to produce large numbers of identical plants for farmers.
• Image size = Magnification x Real size
• Functions of xylem cells: - transport water and mineral ions from the roots to the leaves - lignin for strength
• Functions of phloem cells:

  - transport sugars from the leaves to the rest of the plant

  - Sieve plates allow water carrying food to move freely up and down the plant
• Cell Cycle:

  Stage 1 – cell growth

  Copies of the DNA are made

  Number of organelles (e.g. ribosomes and mitochondria) increase

  Stage 2 - mitosis

  One set of chromosomes is pulled to each end of the cell

  Nucleus divides

  Stage 3 – cytoplasm and cell membranes divide, so cell divides into two identical cells.
• Advantages of therapeutic cloning:

  • cures diseases, produces replacement cells
  • cells unlikely to be rejected
  • cells of any type can be produced
• Disadvantages of therapeutic cloning:

  • risk of transfer of viral infection
  • poor success rate
  • embryo is killed - religious or ethical objections
• A single-celled organism has a relatively large surface area to

  volume ratio. This allows sufficient transport of molecules into and out of the cell to meet the needs of the organism.
• The effectiveness of an exchange surface is increased by:

  • large surface area, more particles can move through resulting in a faster rate of diffusion
  • thin membrane, to provide a short diffusion path
  • efficient blood supply (in animals), creates a steep concentration gradient so diffusion occurs faster
  • ventilation (in animals, for gaseous exchange), creates a steep concentration gradient so diffusion occurs faster
• Osmosis is the diffusion of water from a dilute solution to a

  concentrated solution through a partially permeable membrane.
• Active transport is the movement of particles from an area of low concentration to an area of high concentration against a concentration gradient.
• Differences between active transport and diffusion:

  • Active transport requires energy from respiration, while diffusion requires no energy.
  • Active transport goes against the concentration gradient whereas diffusion goes through the concentration gradient.