3. Movement In & Out of Cells Flashcards
Diffusion definition
Diffusion is the movement of molecules from a region of its higher concentration to a region of its lower concentration
What do molecules move down during diffusion and why?
Molecules move down a concentration gradient, as a result of their random movement
How does a cell membrane affect diffusion?
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
How does the cell membrane filter the molecule? (what is it based on)
The simplest sort of selection is based on the size of the molecules
What does diffusion help living organisms do
Diffusion helps living organisms to:
obtain many of their requirements
get rid of many of their waste products
carry out gas exchange for respiration
What molecules move through the small intestine?
digested food products:
glucose
amino acids
fatty acids
glycerol
From where to where do substances in the small intestine move from and to?
FROM lumen of small intestine
TO blood / lymph in villi found covering small intestine walls
What molecules move through the leaf?
oxygen
carbon dioxide
water vapour
From where to where do substances in the leaf move from and to?
O2
- FROM air spaces between mesophyll cells
- TO mitochondria in all cells
CO2
- FROM air spaces between mesophyll cells
- TO chloroplasts in mesophyll cells
WATER VAPOUR
- FROM stomatal pores
- TO air outside stomata
What molecules move through the lungs?
oxygen
carbon dioxide
From where to where do substances in the lungs move from and to?
O2
- FROM alveolar air space
- TO blood in capillaries around alveoli
CO2
- FROM blood in capillaries around alveoli
- TO alveolar air space
What is the Brownian Motion?
Theory that particles move around randomly
Where does the energy for diffusion come from?
The energy for diffusion comes from the kinetic energy of this random movement of molecules and ions
What factors influence diffusion?
distance
temperature
concentration gradient
How does a cells size affect the surface area to volume ratio? What does this affect?
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
In what ways are cells adapted for diffusion
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)
How does distance affect the rate of diffusion?
The smaller the distance molecules have to travel the faster transport will occur
Examples of cells being adapted for diffusion (distance factor)
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
How does temperature affect the rate of diffusion?
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
How does the concentration gradient affect the rate of diffusion?
The greater the difference in concentration 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 definition
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
What property does a cell membrane have which aids in diffusion? How does it help?
The cell membrane is partially permeable which means it allows small molecules (like water) through but not larger molecules (like solute molecules)
What are plant cells that are full of water called?
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)
Why is turgor pressure useful in plant cells?
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
How can water move into plant cells from soil?
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
How is a concentration gradient formed in plants?
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
Why are the results of osmosis more severe in animal cells?
As animal cells do not have a supporting cell wall, the results on the cell are more severe
What will happen if an animal cell is placed into a strong sugar solution?
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)
What will happen if an animal cell is placed into distilled water?
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
Active transport definition?
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
What is specifically needed for only active transport?
Energy is needed because particles are being moved against a concentration gradient, in the opposite direction from which they would naturally move (by diffusion)
What are examples of active transport?
uptake of glucose by epithelial cells in the villi of the small intestine and by kidney tubules in the nephron
uptake of ions from soil water by root hair cells in plants
How does active transport work?
Active transport works by using carrier proteins embedded in the cell membrane to pick up specific molecules and take them through the cell membrane against their concentration gradient:
Process in steps for active transport
Substance combines with carrier protein molecule in the cell membrane
Carrier transports substances across membrane using energy from respiration to give them the kinetic energy needed to change shape and move the substance through the cell membrane
Substance released into cell
Define diffusion.
Diffusion is the net movement of molecules from a region of its higher concentration to a region of its lower concentration down a concentration gradient as a result of their random movement.
Where does the energy for diffusion come from?
The energy for diffusion comes from the kinetic energy of the random movement of molecules and ions.
Four factors that affect the rate of diffusion and therefore the movement of molecules through membranes:
Distance.
Temperature.
Surface area.
Concentration gradients.
How does surface area affect the rate of diffusion?
As the surface increases, the rate of diffusion increases. This is because there is more space available for the substances to diffuse through.
How does distance affect diffusion?
A greater diffusion distance slows the rate of diffusion as molecules must travel further.
How does temperature affect diffusion?
As temperature increases, the rate of diffusion increases. This is because the molecules gain kinetic energy and thus move faster.
How does the concentration gradient affect the rate of diffusion?
As the concentration gradient increases, rate of diffusion increases.
Describe the importance of diffusion of gases and solutes in living organisms.
obtain many of their requirements.
get rid of many of their waste products.
carry out gas exchange for respiration.
SUMMARY - Basically metabolic reactions.
For how long will diffusing particles spread?
The particles spread out until they are evenly spread and have reached an equilibrium.
State that some substances move into and out of cells by diffusion through the cell membrane. What is the cell membrane?
The cell membrane is a partially permeable membrane therefore it controls the movement of substances in and out of a cell.
How does digested food product diffuse in the small intestine?
Digested food product molecules move from lumen of small intestine to blood/lymph in villi found covering small intestine walls.
How does oxygen diffuse into the leaf?
Oxygen molecules move from air spaces between mesophyll cells to mitochondria in all cells.
How does carbon dioxide diffuse into the leaf?
Carbon dioxide molecules move from air spaces between mesophyll cells to chloroplast in mesophyll cells.
How does water vapor move diffuse into the leaf?
Water vapor moves from stomatal pores to air outside stomata.
How does oxygen diffuse around the body?
Oxygen molecules move from alveolar air space to blood in capillaries around alveoli.
How does carbon dioxide diffuse out of the body?
Carbon dioxide molecules move from blood in capillaries around alveoli to alveolar air space.
Explain 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.
What type of molecules do the cell membrane partially permeable membrane allow through?
The cell membrane is partially permeable which means it allows small molecules (like water) through but not larger molecules (like solute molecules).
Define 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, down the water potential gradient.
What happens if you place a plant cell into a solution that has a higher water potential than the water potential of the cell e.g. distilled water?
When the cell is more concentrated than the surrounding cells, water molecules diffuse into the cell via osmosis, making it turgid.
What happens if you place a plant cell into a solution that has a lower water potential than the water potential of the cell e.g. strong sugar solution?
When it is less concentrated than the surrounding cells, water molecules will leave the cell, making it flaccid leading to plasmolysis (the cell membrane peels away from the cell wall).
What happens if you put a cell into a solution that has the same water potential as the water potential of the cell?
There is no net movement of water in or out of the cell.
What causes a plant to wilt?
If plants do not receive enough water the cells cannot remain rigid and firm (turgid) and the plant wilts.
What prevents the plant cells from taking in too much water and bursting?
Plant cells that are turgid are full of water and contain a high turgor pressure. The pressure created by the cell wall stops too much water from entering and prevents the cell from bursting.
How are plant cells supported by the pressure of water?
When water moves into a plant cell, the vacuole gets bigger, pushing the cell membrane against the cell wall.
Why is it important for plant cells to be firm?
This is important for plants as the effect of all the cells in a plant being firm is to provide support and strength for the plant.
Define turgid.
Cells are described as turgid when they are swollen due to high water content.
Define turgor pressure.
The pressure on the cell wall from the cell membrane pushing upon it. This is a result of the cell becoming turgid as water moves into the cell via osmosis.
Define flaccid.
Occurs when water moves out of the cell via osmosis. The cell shrinks but the cell membrane does not peel away from the cell wall.
Define plasmolysis.
The process by which the cytoplasm pulls away from the cell wall as a result of water loss from the cell.
What happens when an animal cell is placed into a solution that has a higher water potential than the water potential of the cell?
There is a net movement of water into the cell which causes the animal cell to burst.
What happens if you place an animal cell into a solution that has a lower water potential than the water potential of the cell?
There is a net movement of water out of the cell which causes the animal cell to shrink (crenate).
Define 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.
Examples of active transport include:
uptake of glucose by epithelial cells in the villi of the small intestine and by kidney tubules.
uptake of ions from soil water by root hair cells in plants.
