Biology 3 Part 1

Biology 3 Part 1

B3.1
1. Exchanges
  1. Osmosis
    1. The movement of water molecules from a region of high concentration to a region of low concentration through a partially permeable membrane.
    2. Water molecules can diffuse through partially permeable membranes, but sugar molecules and most ions generally cannot.
      1. A cell membrane has specialised molecules to enable some ions and molecules to move into the cell.
    3. A dilute solution contains more water molecules than a concentrated solution. If a partially permeable membrane separates two solutions of different concentrations, there will be net movement of water molecules from the dilute solution to the concentrated solution.
      1. Osmosis explains the movement the movement of water molecules across plant and animal cell membranes. In a plant, water moves from the soil into the root hair cells, because soil water is a more dilute solution than the solution in the cytoplasm of the cell.
      2. Osmosis also happens between animal cells. However, animal cells have no strong cell wall to protect them, so if too much water enters them they burst. If animal or plant cells lose too much water, the cytoplasm shrinks and the cells cannot function properly.
      3. As water continues to enter plant cells by osmosis, the cell contents begin to exert pressure on the cell wall. This is known as turgor pressure. In young plants turgor pressure is the main means of support. When plant cells are placed in a concentrated solution, water leaves the cytoplasm and vacuole by osmosis. Eventually the cytoplasm begins to shrink away from the cell wall. This is known as plasmolysis.
  2. Diffusion
    1. The movement of molecules by random motion of high concentration to a region of low concentration.
    2. The molecules move down the concentration gradient until the concentration becomes the same.
    3. Most substances move into and out of cells by diffusion.
2. Sports Drinks and Active Transport
  1. Active Transport
    1. The movement of particles across a membrane against the concentration gradient (low to high). It requires a protein channel on carrier molecule in the membrane and it uses up energy.
  2. Sports Drinks
    1. Main reason for drinking them is rehydration. The secondary reason for drinking them is ion replacement.
      1. Soft drinks are water and sugar and flavourings, with a sugar content that varies from 0 to 100g per can. It may have Na+ ions- 0 to 150mg per can.
        Athletes in long distance events sweat, which means they are losing water and ions. These need to be replaced. Also they may need glucose to replace that used in muscle respiration. All sports drinks have water and ions and some contain glucose.
  3. Exchange Surfaces
    1. Unicellular organisms have no adaptions because they have a large surface area to volume ration and substances do not need to diffuse very far.
      1. A larger organism like a tapeworm still absorbs substances directly but it is flat so the diffusion distance is not great.
        Earthworms still absorb gasses through the skin but now have a blood supply to take into deeper organs.
        Larger organisms need specialised exchange surfaces. These have the following features:
        Folded to produce a large surface area
        They are thin to give them a short diffusion distance
        A good blood supply to remove substances and maintain the concentration gradient.
3. Absorption of Digested Food
  1. This happens in the ileum of the small intestines
    1. The inner surfaces is folded into villi to increase the surface area.
      1. Epithelium and capillary walls are both one cell thick to create a short diffusion distance.
        Blood receives and removes the digested foods to maintain the concentration gradient.
        Some digested fat enters the lacteal instead of the blood.
4. Gas Exchange in the Alveolus
  1. Single walled blood capillary
  2. Capillary network covers the surface of the alveolus to facilitate oxygen and carbon dioxide exchange
  3. Breathing
    1. Inspiration
      1. Intercostal muscles contract to pull the rib cage upwards and outwards. Diaphragm muscles contract to flatten the diaphragm.
        AS the volume inside the thorax (chest) increases, the pressure inside decreases. When it gets less than atmospheric pressure, air will be drawn into the lungs.
    2. Expiration
      1. The intercostal muscles and the diaphragm relax. The rib cage moves downwards and inwards. The diaphragm moves up into resting dome shape.
        The volume of the thorax goes down so the pressure goes up. When atmospheric pressure is exceeded air moves out from the lungs.
    3. Aids to Breathing
      1. Negative Pressure Ventilators
        This is the iron lung. The patient lies in the machine. The head sticks out one end with an air tight rubber seal at the neck. Air is sucked out so that the pressure around the chest falls. This allows the lungs to be inflated more easily. The vacuum is then released and air rushes in to push the chest in. Air is forced out of the lungs.
      2. Positive Pressure Ventilators
        This involves intubation. A tube is inserted down the trachea. Air is then forced into the lungs to force them to inflate. The process can be useful if the patient is relaxed for surgery. The tube can be inserted via an incision into the trachea directly.
      3. Hand controlled Ventilators
        This consists of a face mask attached to a bag that is squeezed to force the air into the lungs directly.
5. Absorption of Water By Roots
  1. Water is drawn from the soil into the root hair cell by osmosis.
    1. Water crosses the cortex from cell to cell by osmosis as successive vacuoles become diliuted or by capillary attraction between cells.
      1. All water passes through the epidermis cells into the xylem vessels
6. Water Loss from Leaves
  1. When the stomata are open water diffuses out from the saturated air spaces into the atmosphere.
    1. Water then evaporates from the cell surface to keep the air spaces saturated.
      1. This draws water from the vacuoles, concentrating to sap
        This draws water from the adjacent cells by osmosis and subsequently, from the xylem vessels in the leaf veins.
        Water molecules are cohesive (attracted to each other). There fore water drawn out of the xylem pulls up the entire water columns. This is the TRANSPIRATION STREAM.
  2. Factors Affecting Trasnpiration
    1. Temperature- On a warm day water molecules have more kinetic energy. Therefore they evaporate and diffuse faster.
    2. Humidity- If the air already contains a lot of water vapour, diffusion and evaporation is slower.
    3. Air Movement- In still air, water vapour collects a lot of water near the leaf. A breeze will remove this and allows water loss to continue.
    4. Light- Stomata open to allow carbon dioxide for photosynthesis. Therefore they open in light.
      1. Why Guard Cells Open Stomata
        In daylight photosynthesis makes sugar. The vacuole gets more concentrated draws in water by osmosis. The cells curve as they swell to open the pore. At night the sugar is used up and the reverse happens to close the pore.
7. Adaptions To Control Transpiration
  1. The waxy cuticle stops direct evaporation from cells.
    1. Most stomata are on the shaded underside of the leaf.
      1. The lower surface maybe folded with the stomata in the pits.
        Hairs on the surface trap air near the leaf.
        Leaves may be spines with a small surface area.
        Deciduous trees lose leaves when water in the ground is frozen
  2. Phloem
    1. Phloem cells have divided into dense companion cells along side a sieve tube with sieve plates in which sugar is carried.
      1. It is taken to the growing regions and food storage regions faster than expected. This needs engery. Therefore active transport gets the sugar across the plates.

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