Unit 1 - Key Area 2 - Transport Across Cell Membranes Flashcards
What are cell membranes made of?
Proteins and phospholipids.
How are cell membranes selectively permeable?
Because they allow some molecules to pass across but not others.
Describe substance concentration?
Different concentrations of substances exist between cells and their environment.
Important substances such as glucose, carbon dioxide and oxygen must pass into and out of cells following concentration gradients.
Where does passive transport occur?
Passive transport occurs down a concentration gradient and does not require energy.
Give examples of passive transport?
Diffusion and osmosis
What is diffusion?
Diffusion is the movement of molecules down a concentration gradient from a higher concentration to a lower concentration.
Give an example of diffusion?
Sugar cube at the bottom of a cup of tea. Eventually the whole drink is sweet.
What is osmosis?
Osmosis is the movement of water molecules from a higher water concentration to a lower water concentration through a selectively permeable membrane.
What is active transport?
Active Transport is the movement of molecules and ions from a lower concentration to a higher concentration. It requires energy for membrane proteins to move molecules and ions against the concentration gradient.
Explain what happens when an animal cell is placed in a solution with a lower water concentration?
Water moves by osmosis from a higher water concentration inside the cell to a lower water concentration outside the cell causing the cell to shrink.
Explain what happens when an animal cell is placed in a solution with the same water concentration?
Water moves by osmosis into and out of the cell but there is no net gain or loss of water.
Explain what happens when an animal cell is placed in a solution with a higher water concentration?
Water moves by osmosis from a higher water concentration outside the cell to a lower water concentration inside the cell causing the cell to burst.
Explain what happens when a plant cell is placed in a solution with a higher water concentration?
Water moves by osmosis from a higher water concentration outside the cell to a lower water concentration inside the cell causing the cell to become turgid. Plant cell walls prevent bursting.
Explain what happens when a plant cell is placed in a solution with the same water concentration?
Water moves by osmosis into and out of the cell but there is no net gain or loss of water.
Explain what happens when a plant cell is placed in a solution with a lower water concentration?
Water moves by osmosis from a higher water concentration inside the cell to a lower water concentration outside the cell causing the cell to become plasmolysed. Plant cell walls prevent cell shrinkage.
