Biology Unit 2

• What does the cell membrane control in a cell?


  It controls which substances enter or leave the cell.
• What is meant by the term 'selectively permeable' in relation to the cell membrane?


  It allows some substances through while preventing others from passing.
• What essential materials enter the cell?

  Oxygen, carbohydrates, and amino acids.
• What waste product leaves the cell?


  Carbon dioxide.
• What is the role of the cell wall in plant cells?


  The cell wall is totally permeable and does not control what enters or leaves the cell.
• How does diffusion transport substances in cells?


  It is the movement of molecules from a region of high concentration to a region of low concentration.
• What factors affect the rate of diffusion?


  Temperature, surface area, and concentration gradient.
• What is the definition of osmosis?


  Osmosis is the diffusion of water molecules through a selectively permeable membrane.
• How does osmosis differ from diffusion?


  Osmosis specifically involves the movement of water molecules.
• What happens to water molecules during osmosis in relation to solute concentration?


  Water moves from a dilute solution to a more concentrated solution.
• What is the net movement of water when a cell is surrounded by pure water?

  Water moves into the cell because there is a higher concentration of free water molecules outside the cell.
• What occurs to an animal cell placed in a hypotonic solution?


  Water moves into the cell, causing it to swell and potentially burst.
• What is cell lysis?


  It is the bursting of a cell due to excessive water intake.
• What happens to an animal cell in a hypertonic solution?


  Water moves out of the cell, causing it to shrink or crenate.
• What is the effect of an isotonic solution on red blood cells?


  There is no net movement of water, so the cells remain the same size.
• What is the importance of water in human cells?


  Water is found in the cytoplasm, tissue fluid, and blood, affecting cell function.
• What happens to red blood cells in a hypotonic solution?


  They gain water and may swell and burst, leading to cell lysis.
• What is turgidity in plant cells?


  Turgidity is the state of being swollen or firm due to water pressure against the cell wall.
• What happens to a plant cell in pure water?


  Water moves into the cell, making it turgid.
• What role does the cell wall play in plant cells during osmosis?


  The cell wall limits further entry of water and prevents the cell from bursting.
• What is plasmolysis in plant cells?


  Plasmolysis occurs when water leaves the cell, causing the cell membrane to pull away from the cell wall.
• What happens to a plant cell in a concentrated solution?


  The plant cell loses water and becomes plasmolysed and flaccid.
• What are the steps to prepare a slide of onion tissue for microscopy?


  • Peel a small piece of onion epidermis.
  • Place it on a microscope slide with a few drops of iodine.
  • Use forceps to lower a coverslip onto the slide.
  • Avoid trapping air bubbles.
• How do you focus a microscope slide?


  1. Place the slide on the stage and secure it.
  2. Start with low power for a wider field of view.
  3. Use the coarse focussing knob to find the specimen.
  4. Switch to higher power and use the fine focus knob for clarity.
• What changes occur in Visking tubing during osmosis experiments?


  • In Beaker A: Visking tubing with water decreases in mass in 20% sucrose.
  • In Beaker B: Visking tubing with 20% sucrose increases in mass in water.
• What is the effect of turgor pressure in plant cells?


  Turgor pressure provides support and keeps the plant upright.
• What happens to plant cells when they are not turgid?


  They are described as flaccid and can lead to wilting.
• What is the significance of the concentration of water in blood for red blood cells?


  It affects the function of red blood cells in carrying oxygen.
• How does temperature affect osmosis?


  Temperature can increase the rate of osmosis.
• What is the role of solutes in osmosis?


  Solutes attract water molecules, affecting their movement.
• How does the presence of a cell wall affect osmosis in plant cells compared to animal cells?


  The cell wall prevents plant cells from bursting, unlike animal cells which can lyse.