Chapter 3 - Transport in Cells

• What is diffusion?

  The net movement of particles from an area of high concentration to an area of low concentration.
• One example of diffusion in the human body happens in the alveoli. State the four ways in which they are adapted to conduct diffusion effectively.

  • Large surface area
  • Very thin (one-cell thick)
  • Moist lining
  • Good blood supply
• What are three factors that effect the rate of diffusion?

  • Temperature
  • Concentration
  • Surface Area
• Explain why diffusion takes place faster when there is a higher temperature.(2)

  The particles have more energy, so they move around a lot faster.
• What is osmosis?

  Osmosis is the movement of water molecules from an area of low concentration to an area of high concentration across a partially-permeable membrane.
• What is the difference between osmosis and diffusion?

  Osmosis only works in water whereas diffusion works for any particles in a gas or liquid.
• True or false? Water molecules pass through a membrane in only one direction during osmosis?

  False - Water molecules move about randomly, so they pass both ways through a membrane during osmosis
• Where is there a high concentration of oxygen in the body?

  In the alveoli
• Where is there a high concentration of carbon dioxide in the body?

  In the capillary
• What is the advantage of the alveolus wall being one cell thick?

  It provides a short diffusion pathway
• Why is there always a low concentration of oxygen in the blood stream?

  The oxygenated blood is always moving away from the alveoli and de-oxygenated blood is replacing it
• What is active transport?

  The movement of particles across a partially-permeable membrane from an area of low concentration to high concentration, requiring energy
• In what cell does active transport takes place?

  Root hair cell
• What process allows substances to be absorbed against a concentration gradient?

  Active transport
• How does active transport differ from diffusion?

  Active transport moves substances against the gradient
• What is the energy source for active transport?

  Energy from respiration
• Why can't sugars diffuse into the cell from the lumen?

  Because their concentration is higher inside
• What role do mitochondria play in active transport?

  They provide energy needed for the process
• What ions do root hair cells transport into plants?

  Magnesium ions
• Describe the process of active transport in the human small intestine.

  1. Sugars like glucose are present in lower concentration in the lumen.
  2. Active transport moves glucose into the intestinal cells.
  3. Glucose is then transported into the blood for distribution.
• Explain how root hair cells utilize active transport.

  • Root hair cells absorb magnesium ions from the soil.
  • Active transport moves these ions into the cells against the concentration gradient.
  • Ions are then transported to the xylem for distribution to leaves.
• What does the term "net movement" mean in diffusion?

  Overall movement from high to low concentration
• What are the three molecules that move in and out of cells by diffusion?

  • Oxygen
  • Carbon dioxide
  • Urea
• How does the concentration of oxygen outside the cell compare to inside?

  Higher concentration outside than inside
• What happens to oxygen molecules during diffusion?

  They move into the cell from outside
• How does the concentration of carbon dioxide inside the cell compare to outside?

  Higher concentration inside than outside
• Why does higher temperature increase diffusion rates?

  Particles have more kinetic energy and move faster
• Which cell has a greater rate of diffusion, one with a large surface area or one with a small surface area?

  The cell with a large surface area
• What type of membrane allows osmosis to occur?

  Partially permeable membrane
• What does a dilute sugar solution contain a lot of?

  Water molecules
• What is the concentration of water in a concentrated sugar solution?

  Low concentration of water
• How does osmosis affect an animal cell placed in pure water?

  The cell expands and may burst
• What happens to an animal cell in a concentrated solution?

  Water moves out, causing the cell to shrink
• What is the effect of osmosis on a plant cell placed in water?

  The cell becomes turgid and swollen
• What prevents a plant cell from bursting when it becomes turgid?

  The cell wall
• What happens to a plant cell in a concentrated solution?

  The cell shrinks and becomes flaccid
• Why do cells need oxygen?

  For respiration to generate energy
• How does the concentration of oxygen outside the cell compare to inside?

  Higher concentration outside than inside
• What happens to oxygen molecules during diffusion?

  They move into the cell from outside
• What is produced as a waste gas during respiration?

  Carbon dioxide