1.3 Cell Transport

• Diffusion is the net movement of particles of a gas or solute from an area of higher concentration to an area of low concentration (down a concentration gradient).
• What is diffusion?


  The net movement of particles of a gas or solute from an area of higher concentration to an area of low concentration (down a concentration gradient).
• Oxygen molecules diffuse into the blood through the alveoli.
• Food molecules diffuse into the bloodstream through the small intestine.
• Minerals and water diffuse into plants through the roots.
• Water molecules diffuse into the bloodstream through the large intestine.
• Perfume diffuses from one side of the room to spread out everywhere.
• What factors increase the rate of diffusion into the cell?

  Increasing temperature, increasing concentration gradient, decreasing amount of substance inside the cell, having lots of infolding in the cell membrane, adding more water inside the cell (diluting inside), increasing surface area, increasing substance outside the cell
• Decreased temperature, decreased surface area, decreased concentration gradient all decrease the rate of diffusion.
• Higher temperature gives particles more kinetic energy so they move faster.
• Higher surface area means more particles can enter the cell in the same time period.
• Diffusion relies on the random movement of particles. A bigger difference in concentration means overall more particles will diffuse from higher to lower concentration.
• Diffusion is very slow, so if the diffusion distance is shorter, it will take less time for the substance to diffuse into the cell.
• Osmosis is the diffusion of water from an area of higher water potential to an area of lower water potential through a partially permeable membrane.
• Higher water potential is a dilute solution with higher water concentration.
• Lower water potential is a concentrated solution with a lower water concentration.
• Partially permeable is when a membrane is selective, some substances can pass through and others cannot.
• The only substance that can undergo osmosis is water.
• A very concentrated salt solution has less water and more salt. A more diluted solution has more water as it has less salt molecules.
• percentage change in mass = final value - original value / original value x 100
• In pure water (higher water concentration outside cells), an animal cell undergoes lysis.
• In pure water (higher water concentration outside cells), an plant cell becomes turgid.
• In concentrated salt solution (higher water concentration inside cells), an animal cell becomes plasmolysed.
• In concentrated salt solution (higher water concentration inside cells), a plant cell becomes plasmolysed.
• When an animal cell undergoes lysis (in pure water), water moves into cell so much that it bursts.
• When an animal cell becomes plasmolysed (in concentrated salt solution), the cytoplasm is primarily water so when it diffuses out, the cell shrinks.
• When a plant cell becomes turgid (in pure water), the water diffuses into the cell and it expands and rounds the cell wall.
• When a plant cell becomes plasmolysed (in concentrated salt solution), the cytoplasm shrinks but the cell wall stays the same.
• What is active transport?

  The movement of a substance from an area of lower concentration to an area of higher concentration (against a concentration gradient) across a membrane USING ENERGY.
• How do crocodiles make use of active transport?

  They pump salt out of their body through their neck glands.
• Explain why cells that carry out a lot of active transport also usually have lots of mitochondria?

  Mitochondria is the site of respiration, energy is needed to carry out active transport therefore more mitochondria > more energy > more active transport
• An example of when active transport is used in the digestive system?

  Glucose is actively transported from the small intestine into the bloodstream.
• The rate of active transport depends on the rate of respiration.
• Active transport uses energy whereas diffusion and osmosis do not.
• Active transport needs energy, energy is produced through respiration which uses up oxygen, therefore cells have a high oxygen requirement.
• SA to V ratio is how many times larger or smaller the SA is compared to the V.
• An exchange surface is a location where materials are transferred between an organism and its environment.
• A transport system is a structure that moves materials around the body of a multicellular organism.
• As an organism gets larger, the SA to V ratio gets smaller, so the rates of diffusion are slower. The diffusion distance is too large for substances necessary for the cells to reach them. Therefore, large organisms require exchange surfaces and transport systems.
• Single-celled organisms have a large SA to V ratio. There is a fast diffusion rate meaning they get enough nutrients to survive.