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B2 Movement in and out of cells - Coggle Diagram
B2 Movement in and out of cells
Examples of diffusion in living organisms
:
Site
: small intestine
Molecules moving
:digested food products - glucose, amino aicids, fatty acids,and glycerol etc.
From
: lumen of small intestine
To
: blood/lymph in villi found covering small intestine walls
Site
: leaf
Molecules moving
: water vapour
From
: stomatal pores
To
: air outside of stomata
Site
: lungs
Molecules moving
: oxygen
From
:alveolar air space
To
: blood in capillaries arround alveoli
Site
: leaf
Molecules moving
: carbon dioxide
From
: air spaces between mesophyll cells
To
: chloroplasts in mesophyll cells
Site
: lungs
Molecules moving
: carbon dioxide
From
: blood in capillaries around alveoli
To
: alveolar air space
Site
: leaf
Molecules
moving
: oxygen
From
: air spaces between mesophyll cells
To
: mitochondria in all cells
Factors that afect the rate of diffusion
Surface area to volume ratio
:
The bigger a cell or structure is, the smaller its surface area to volume ratio is, slowing down the rate at which substances can move across its surface
Many cells which are adapted for diffusion have increased surface area in some way – eg root hair cells in plants (which absorb water and mineral ions) and cells lining the ileum in animals (which absorb the products of digestion)
Distance
:
The smaller the distance molecules have to travel the faster transport will occur
This is why blood capillaries and alveoli have walls which are only one cell thick, ensure the rate of diffusion across them is as fast as possible
Temperature
:
The higher the temperature, the faster molecules move as they have more energy
This results in more collisions against the cell membrane and therefore a faster rate of movement across them
Concentration Gradient
The greater the difference in concentration on either side of the membrane, the faster movement across it will occur
This is because on the side with the higher concentration, more random collisions against the membrane will occur
Osmosis
All cells are surrounded by a cell membrane which is partially permeable
Water can move in and out of cells by osmosis
Osmosis is the net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane
In doing this, water is moving down its concentration gradient
The cell membrane is partially permeable which means it allows small molecules (like water) through but not larger molecules (like solute molecules)
Diffusion
Diffusion is the movement of molecules from a region of its higher concentration to a region of its lower concentration
Molecules move down a concentration gradient, as a result of their random movement
For living cells, the principle of the movement down a concentration gradient is the same, but the cell is surrounded by a cell membrane which can restrict the free movement of the molecules
The cell membrane is a partially permeable membrane – this means it allows some molecules to cross easily, but others with difficulty or not at all
The simplest sort of selection is based on the size of the molecules
Diffusion helps living organisms to
:
obtain many of their requirements
get rid of many of their waste products
carry out gas exchange for respiration
Osmosis in plant tissues
Plant cells that are turgid are full of water and contain a high turgor pressure (the pressure of the cytoplasm pushing against the cell wall)
This pressure prevents any more water entering the cell by osmosis, even if it is in a solution that has a higher water potential than inside the cytoplasm of the cells
This prevents the plant cells from taking in too much water and bursting
Plant roots are surrounded by soil water and the cytoplasm of root cells has a lower water potential than the soil water
This means water will move across the cell membrane of root hair cells into the root by osmosis
The water moves across the root from cell to cell by osmosis until it reaches the xylem
Once they enter the xylem they are transported away from the root by the transpiration stream, helping to maintain a concentration gradient between the root cells and the xylem vessels
If plants do not receive enough water the cells cannot remain rigid and firm (turgid) and the plant wilts
Osmosis in animal tissues
Animal cells also lose and gain water as a result of osmosis
As animal cells do not have a supporting cell wall, the results on the cell are more severe
If an animal cell is placed into a strong sugar solution (with a lower water potential than the cell), it will lose water by osmosis and become crenated (shrivelled up)
If an animal cell is placed into distilled water (with a higher water potential than the cell), it will gain water by osmosis and, as it has no cell wall to create turgor pressure, will continue to do so until the cell membrane is stretched too far and it bursts
The importance of water as a solvent
Dissolved substances can be easily transported around organisms – eg xylem and phloem of plants and dissolved food molecules in the blood
Digested food molecules are in the alimentary canal but need to be moved to cells all over the body – without water as a solvent this would not be able to happen
Toxic substances such as urea and substances in excess of requirements such as salts can dissolve in water which makes them easy to remove from the body in urine
Water is also an important part of the cytoplasm and plays a role in ensuring metabolic reactions can happen as necessary in cells
Water is important for all living organisms as many substances are able to dissolve in it (it is a solvent)