Biology P1

• What are Sub-cellular structures

  Structures inside cells
• Sub-cellular structures in an animal cell


  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Mitochondria
  • Ribosomes
• Additional sub-cellular structures in plant cells

  • Cell wall
  • Permanent vacuole
  • Chloroplasts
• Prokaryotic cells


  Cells without a nucleus, where the genetic material is not enclosed in a nuclear membrane
• Eukaryotic cells


  Cells with a nucleus and membrane-bound organelles
• Eukaryotic cells

  • Plant cells
  • Animal cells
  • Fungal cells
• Differences between prokaryotic and eukaryotic cells

  • Prokaryotic cells are smaller
  • Prokaryotic cells lack membrane-bound organelles like mitochondria and chloroplasts
  • Prokaryotic DNA is a single loop rather than being enclosed in a nucleus
• Plasmids


  Small, circular DNA molecules in bacterial cells that can replicate independently of the main chromosome
• Flagella


  Tail-like structures that help some bacteria move
• The size of cells is often given in micrometres (μm)
• Magnification

  How many times larger the image is than the real object
• Calculating magnification

  Magnification = size of image / size of real object
• Cellular structures ordered by size, largest first

  • Liver cell
  • Bacterium
  • Nucleus
  • Ribosome
• Calculating magnification of a drawing


  Magnification = size of drawing / actual size of object
• Chromosomes


  DNA molecules that carry genetic information
• Mitosis

  Cell division to form two genetically identical daughter cells
• Stem cells

  Undifferentiated cells that can divide to form different cell types
• Types of stem cells

  • Embryonic stem cells
  • Adult stem cells
• Therapeutic cloning

  Creating a cloned embryo as a source of stem cells for treating the patient
• Diffusion

  The net movement of particles from an area of high concentration to an area of low concentration
• Diffusion occurs because particles move randomly and spread out
• Examples of diffusion in living organisms

  • Oxygen and carbon dioxide in gas exchange
  • Urea from cells into blood
  • Digested food molecules into blood
• Factors affecting diffusion rate

  • Concentration gradient
  • Temperature
  • Surface area of membrane
• Osmosis


  The diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane
• Active transport

  The movement of substances against a concentration gradient, requiring energy
• The independent variable is the sugar concentration, the dependent variable is the change in mass
• Concentrated solution

  Contains less water
• Dilute solution

  High concentration of water
• Partially permeable membrane


  • Net movement of water molecules
  • These molecules are too large to pass through the membrane
• How to investigate the effect of sugar concentration on plant cells

  1. Place the potato cylinders in the solutions

  2. After 30 minutes, measure the change in mass
• Independent variable


  The concentration of sugar, deliberately changed
• Dependent variable

  The change in mass of the potato cylinders
• If the potato cylinders do not lose or gain water, then the sugar solution must be the same concentration as the potato tissue
• Active transport


  • Moves substances against a concentration gradient, from an area of low concentration to high concentration
  • Requires energy from respiration
  • Allows mineral ions to be absorbed into plant root hairs from very dilute solutions in the soil
  • Allows sugar molecules to be absorbed from lower concentrations in the gut into the blood, which has a higher concentration
• A person opens a bottle of perfume. People in the room smell it faster on a warm day
• Substances need energy from respiration to be absorbed against a concentration gradient
• In addition to a large surface area, one other feature that makes an exchange surface more efficient is a short diffusion distance
• Epidermis


  Covers the outer surfaces of the plant for protection
• Palisade mesophyll


  The main site of photosynthesis in the leaf
• Spongy mesophyll


  Air spaces between the cells allow gases to diffuse through the leaf