Transport in cells Flashcards
Diffusion definition
The net movement of particles from an area of high concentration to an area of low concentration down a concentration gradient across a partially permeable membrane, until equilibrium is reached.
It is a passive process, meaning it requires no energy.
Why do some organisms need specialised exchange surfaces ?
Large multicellular organisms have a small SA : V ratio. This means that they have several layers of cells between the centre and the environment. Therefore, substances will take longer to diffuse, and may be used up by outer layers before they reach inner cells.
Factors that aid rate of diffusion
Steep concentration gradient
Large surface area to increase site of exchange
Thin membrane to provide short diffusion path.
Osmosis defintion
The movement of water molecules from a dilute region to a concentrated region, down a concentration gradient, across a partially permeable membrane.
What is a dilute solution ?
When there is a high water concentration
What is a concentrated solution ?
When there is a low water concentration
Hypotonic solution
More water outside cell than inside
Water moves into cell via osmosis
Dilute solution
Hypertonic solution
More water inside the cell than outside
Water leaves cell via osmosis
Concentrated solution
Isotonic solution
Equal amounts of water inside + outside the cell
No net movement
What happens when an animal cell is in a hypertonic solution ?
Water leaves the cell via osmosis across a PPM
Cell shrivels
CRENATION
What happens when an animal cell is in a hypotonic solution ?
Water enters the cell via osmosis across a PPM
Cell burst as too much water moves in
LYSIS
What happens when a plant cell is in a hypertonic solution ?
Water leaves the vacuole via osmosis
Some water is left - leaving the cell with a less rigid shape and smaller vacuole
FLACCID
Cell eventually has no/little water left - very small vacuole, cell membrane and cytoplasm pulls away from cell wall
PLASMOLYSED
What happens when a plant cell is in a hypotonic solution ?
Water enters the vacuole via osmosis across a PPM
Cell gains lots of water so swells
Will not burst due to rigid cell wall
TURGID
What is active transport ?
The net movement of particles from a region of low concentration to high concentration against the concentration gradient across a partially permeable membrane. Requires energy in the form of ATP, released by respiration in the mitochondria
Practical method to investigate the effect of concentrations of sugar solutions on the mass of plant tissue
Set up 6 boiling tubes, each containing the same volume of one of the sucrose solutions.Label the boiling tubes.
Prepare 6 potato cylinders using a borer and cut the cylinders to the same length. Gently dry each potato cylinder using a paper towel to remove excess liquid and record its mass before placing it into one of the boiling tubes.
Leave the potato cylinders in the boiling tubes for 40 minutes.
Remove each potato cylinder from its boiling tube, gently remove excess liquid from the surface of the cylinder with a paper towel and record its mass.
If possible, repeat the experiment to obtain multiple values of mass change for each solution.
Properties of the waxy cuticle
Water proof
Stops water evaporating out the leaf
Properties of the upper epidermis
Protective barrier against damage and pathogens
Translucent - lets light through to palisade mesophyll
Properties of palisade mesophyll layer
Site of photosynthesis
Regular box like structure to maximise photosynthesis
Contains 80% of chloroplasts
Chloroplasts lie at the top of the layer
Properties of the spongy mesophyll layer
Less tightly packed
Irregular shaped cells
Contains 20% of chloroplasts
Air spaces for gas exchange
Properties of lower epidermis
Protective layer
Contain guard cells - open and close stomata, open to let carbon dioxide in for photosynthesis, close to stop water loss
Properties of vascular bundle
Contain xylem - transports water and mineral ions
Contains phloem - transports amino acids and sucrose
What are xylem ?
Mature xylem consists of elongated dead cells, arranged end to end to form continuous vessels.
Properties of xylem vessels
Contain no cytoplasm
Have tough walls containing lignin that builds up in spirals in the cell wall. Lignin makes spirals very strong, to withstand the pressure from water and provide support.
The contents and end walls break down to form a hollow centre, called a lumen.
What is a transpiration stream ?
The process that carries water and mineral ions from the roots into the leaves ( one direction ).
What happens to guard cells in bright light ?
Potassium ions move into the guard cells via active transport
This makes the guard cells more concentrated than the surrounding tissues.
Water moves into the guard cells via osmosis across a PPM.
Cells swell unevenly because the thicker inner cell wall is less flexible than the thinner outer wall.
Potometer required practical to measure rate of photosynthesis
The potometer is filled with water.A shoot is cut from a woody plant. The end of the shoot is cut under water to ensure that the xylem remains water-filled and prevents air locks.
The shoot is inserted into the rubber tubing at the end of the potometer.
The potometer is raised so that a bubble of air is taken up.
The potometer is lowered into the water. The distance travelled by the air bubble is recorded over a period of time.
Effects of light intensity on transpiration
Increased light = increased rate of photosynthesis
Plant needs more CO2, so stomata opens to let gas in.
More stomata open = more water lost by transpiration
Effects of temperature on transpiration
Increased temperature = increased kinetic energy of water molecules in leaf
Water molecules move more so are more likely to be lost via transpiration
Effects of humidity on transpiration
High humidity = closer to equilibrium = lower concentration gradient
Slows down rate of transpiration
Effects of wind speed on transpiration
Carries away water molecules from the leaf.
High conc. gradient as lots of water inside, but not outside, so water leaves by transpiration down a concrete. gradient
What are phloem ?
Made up of living cells lined end to end. They contain cytoplasm.
What does phloem transport ?
Sucrose + amino acids up and down the plant.
This is called translocation.
Substances are either immediately used up or stored.
Where does translocation occur ?
Between where substances are made ( sources ), and where they are used up ( sinks )
Where is sugar in plants made ?
The leaf
Where is sugar in plants stored ?
In the roots as starch
What are companion cells ?
Found along the outside of the phloem vessel. Contain nuclei and mitochondria to provide energy for translocation.
What reduces the resistance of flow in phloem vessels ?
Limited amount of cytoplasm
No nucleus or vacuole
What allows movement of substances through the phloem vessel ?
Perforated sieve plates
What allows substances to be transported all around the plant by translocation ?
A two way flow
What is repeatability ?
The measure of the likelihood that, having produced one result from an experiment, you can try the same experiment with the same result.
A way for researchers to check their own results are true.
What is reproducibility ?
Whether results in a paper can be attained by a different research team, using the same method.
Shows that the results attained are not artifacts of the unique set up in one research lab.
How is light a limiting factor of photosynthesis ?
Increasing light intensity increases the rate of photosynthesis, so light intensity is the limiting factor.
After a certain point, increasing light does not increase rate of photosynthesis, meaning that something else is the limiting factor.
How is CO2 a limiting factor of photosynthesis ?
Increasing CO2 concentration increases the rate of photosynthesis, so CO2 concentration is the limiting factor.
After a certain point, increasing CO2 does not increase rate of photosynthesis, meaning that something else is the limiting factor.
How is temperature a limiting factor of photosynthesis ?
Increasing temperature increases rate of photosynthesis, as enzymes and reactants have more kinetic energy, meaning it is the limiting factor.
At the optimum temperature, there is the highest rate of photosynthesis.
After the optimum temperature, rate decreases as enzymes denature, as there is too much kinetic energy.
How is chlorophyll a limiting factor of photosynthesis ?
The more chlorophyll, the higher the rate of photosynthesis as chlorophyll id needed for reactions.
Increased amount of glucose = more protein = increased growth.
How to test for starch
Mix food with iodine.
If present, turns orange to blue/black
How to test for glucose
Mix food with Benedict solution, and heat in a hot water bath for 3 minutes.
If present, turns blue to a brick red precipitate.
How to test for protein
Mix food with biuret solution and leave for 2 minutes.
If present, turns blue to purple
How to test for lipids
Mix food with ethanol and add to cold water.
If present, turns colourless to milky.
Effect of temperature on enzymes
As temp increases, kinetic energy increases, meaning more successful collisions.
Optimum temp is body temp.
Above this, the shape of the active site is changed as bonds are broken ( denatured ). This means the substrate can no longer fit, so the reaction rate is 0.
Effect of enzyme concentration on rate of reaction
Increasing enzyme conc. increases the available active sites, therefore increasing the rate of reaction as more successful frequent collisions can occur.
This is true until there are more enzymes than substrates, meaning that the limiting factor is the substrate.
Effect of pH on enzymes
Enzymes have an optimum pH. If the pH becomes too acidic or alkaline, the rate of reaction will decrease. The incorrect pH will denature an enzyme.
