MOVEMENT IN AND OUT OF MOLECULES Flashcards
Diffusion
The net movement of particles from a region of their higher concentration to a region of their lower concentration down a concentration gradient, as a result of their random movement
Active transport
The movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration using energy from respiration
Osmosis
The net movement of water molecules from a region of higher water potential (a dilute solution) to a region of lower water potential (a concentrated solution) through a partially permeable membrane.
Diffusion imporatnce
Diffusion is a really important process for living organisms because it helps to provide essential gases and solutes (materials in solution) and also helps to remove some substances that are potentially toxic (poisonous). These move in or out of the cell through the cell membrane.
The energy for diffusion comes from the kinetic energy (movement energy) of the random movement of molecules and ions. From the organism’s point of view, it is a ‘free’ process – no energy needs to be provided to make it happen.
factors that help diffusion to be efficient. These are:
- Distance (the shorter the better), e.g. thin walls of alveoli and capillaries.
- Concentration gradient (the bigger the better). This can be maintained by removing the substance as it passes across the diffusion surface. (Think about oxygenated blood being carried away from the surface of alveoli.)
- Size of the molecules (the smaller the better).
- Surface area for diffusion (the larger the better), e.g. there are millions of alveoli in a lung, giving a huge surface area for the diffusion of oxygen.
- Temperature (molecules have more kinetic energy at higher temperatures).
osmosis
Plants rely on osmosis to obtain water through their roots. They use water as a transport medium (to carry mineral salts, sucrose and amino acids around the plant) and to maintain the turgidity of cells (their firmness). When young plants lose more water than they gain,
Effects of osmosis on plant and animal tissues.
- When placed in water, plant and animal cells will take in the water through their cell membranes by diffusion. The diffusion of water in this way is called osmosis.
- Plant cells become turgid (swollen), but do not burst because of their tough cell wall.
- Plants are supported by the pressure of water inside the cells pressing outwards on the cell wall.
- Animal cells will burst, because they have no cell wall. • The reverse happens when plant and animal cells are placed in concentrated sugar or salt solutions.
- Plant cells become flaccid (limp).
- Animal cells also become flaccid.
water potential
• When placed in water, plant and animal cells will take in the water through their cell membranes because there is a higher water potential outside the cells than inside. • Plant cells become turgid (swollen), but do not burst because of their tough cell wall. A turgor pressure is created, which will restrict any further entry of water into the cell. • Plants are supported by the pressure of water inside the cells pressing outwards on the cell wall, which is inelastic and prevents further net entry of water. • Animal cells will burst, because they have no cell wall. • The reverse happens when plant and animal cells are placed in concentrated sugar or salt solutions. This is because there is a higher water potential inside the cell than outside it. • Plant cells become flaccid (limp) and the cytoplasm is no longer pressed against the cell wall. The process of water loss from a cell when it is placed in a solution with a lower water potential is called plasmolysis. • When animal cells become flaccid, their shape can change – they can become crenated.
active transport
Active transport is the movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration using energy from respiration. Animals and plants rely on active transport to move some substances because the concentration gradient is not always the right way round for diffusion. However, cells need to provide energy to achieve movement by active transport. This energy is supplied through respiration using adenosine triphosphate (ATP). Mitochondria (cell organelles in the cytoplasm) control energy release. Respiratory poisons block energy release, so they can prevent active transport. Protein molecules in the cell membrane play an important part in moving particles across the membrane. The protein binds with ATP, which breaks down to provide energy to move the particles against their concentration gradient.
are two big differences between diffusion and active transport:
- direction of movement (down a gradient, or up a gradient);
- whether or not energy is needed for the movement.
Examples of active transport
