1.2 Transport Across Membranes Flashcards
What is the cell membrane mad out of?
Phospholipids
and proteins
Selectively permeable
The property of a membrane that controls the movement of molecules depending on their size.
Impermeable
Very large molecules such as proteins are too big to move through the cell membrane, which is said to be impermeable to them.
What are proteins in the cell membrane used for?
Protein molecules are found embedded in the two layers of phospholipids. Membrane proteins have a wide variety of functions.
Some allow a cell to respond to specific chemical signals from other cells, others are enzymes, and some proteins are involved in the transport of substances across the cell membrane.
Concentration gradient
The difference in concentration between two solutions, between different cells, or between cells and a surrounding solution.
Diffusion
Diffusion is the net movement of molecules from an area where they are at a higher concentration to areas where they are at a lower concentration.
The cell membrane is composed of
lipid and protein
The difference in concentration of a substance is a
concentration gradient
Osmosis
The movement of water molecules across a partially-permeable membrane from a region of low solute concentration to a region of high solute concentration.
An animal cell placed in a solution with a water concentration higher than that inside the cell will
take up water by osmosis and could burst
An animal cell placed in a solution with a lower water concentration than that inside the cell will
lose water by osmosis and could shrink.
A plant cell placed in a solution with a lower water concentration than that inside the cell will
take up water by osmosis and become turgid
A plant cell placed in a solution with a lower water concentration than that inside the cell will
lose water by osmosis and become plasmolysed.
Plasmolysed
Description of a plant cell in which the vacuole has shrunk, and the membrane has pulled away from the wall due to water loss by osmosis.
Turgid
Plant cells placed in a solution with a high water concentration compared to their contents (e.g. pure water) will gain water by osmosis and swell up until their cytoplasm and cell membrane are pushing against their cell wall.
Passive transport
The movement of molecules down a concentration gradient without the need for additional energy e.g. diffusion and osmosis.
Active transport
This occurs when molecules are moved across the cell membrane from an area where they are at a low concentration to an area where they are at a high concentration by specific transport proteins. Proteins require an energy supply. Energy is provided by the breakdown of ATP inside the cell.
