B1 Diffusion Osmosis Active Transport Flashcards
Diffusion
The spreading out of particles from an area of higher concentration to an area of lower concentration
Why does diffusion only happen in solutions and gases
The particles in these substances are free to move randomely
Factors which affect rate of diffusion
Temperature
Concentration gradient
Surface area
How does temperature increase rate of diffusion
Particles have more energy
How does concentration gradient affect the rate of diffusion
The greater the concentration gradient, the quicker diffusion takes place
When there is large difference in concentration between 2 regions particles will move more quickly from area of high concentration to area of low concentration
How does surface area affect rate of diffusion
As the surface area of the membrane increases, the rate of diffusion also increases
As there is more space for molecules to diffuse across the membrane
How to predict which way substances will move across a cell membran
Molecules travel across the membrane in the direction determined by their concentration gradients
Osmosis
The movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration
Why is diffusion important
So particles can move from 1 side of the room to another
Why is it important for multicellular organisms to have exchange surfaces and transport systems
In order for substances to pass in and out of the cells
How are exchange surfaces adapted for sufficient molecules to be transported in and out of cells
Large surface area
Why is diffusion passive process
No energy is needed
Concentration gradient
A difference in concentration between 2 areas
What happens to surface area to volume ratio as object gets bigger
Decreases
How do root hairs take in water from soil
Osmosis
What happens to a plant cell when it is placed in a more DILUTE solution?
The cell gains water by osmosis but does not burst
This cell is now turgid
What happens to an plant cell when it is placed in a more CONCENTRATED solution
Cell loses water by osmosis
Cell membrane pulls away from the cell wall
This is is called plasmolysis.
What happens to an animal cell when it is placed in a more DILUTE solution
The cell gains water by osmosis and may burst. This is called lysis.
What happens to an animal cell when it is placed in a more CONCENTRATED solution
The cell loses water by osmosis shrivels. This is called crenation.
Why does a plant cell not burst when it is placed in a more dilute solution
The plant cell has a cell wall
Differences between osmosis and diffusion
Diffusion is movement of particles and osmosis is movement of water
Diffusion does not require a membrane osmosis does
Diffusion driven by concentration gradient of particles but osmosis driven by concentration gradient of water
When they reach equilibrium
Isotonic solution
A solution which has same concentration of solutes as the inside of a cell
What happens when a cell placed us isotonic solution
No net movement of water across cell membrane as concentration of solutes equal inside and outside the cell
Water moves in and out of cell at same rate so cell’s size remains stable
Hypotonic solution
Solution with a lower solute concentration compared to the inside of the cell
What happens when cell placed in hypotonic solution
Water will move into the cell as concentration of water is higher outside the cell and lower inside the cell
Cell could burst (lyse) if too much water enters
Hypertonic solution
Solution with a higher solute concentration compared to the inside of the cell
What happens when cell placed in hypertonic solution
Water will move out of cell as concentration of water is lower outside the cell and higher inside the cell
As water leaves cell shrinks (crenate in animals or plasmolyze plant cells) as loses water
Movement of water isotonic, hypotonic and hypertonic solution
Isotonic - No net water movement, cell remains the same size
Hypotonic - Water enters the cell, causing it to swell
Hypertonic - Water leaves the cell, causing it to shrink
What happens to animal cells when they lose or gain too much water
They stop working properly
Why maintaining constant internal conditions in living organisms is important
Enzymes only function properly under a small range of certain conditions, such as preferred pH and temperature
If enzymes cannot function this could cause organism to die
What happens if plant loses too much water
They become soft
Use osmosis to explain the effect of placing plant tissue in salt or sugar solutions
The cells will shrink if placed in a solution of sugar or salt in water due to osmosis
Explain the mechanisms that lead to turgid or flaccid plant cells and plasmolysis
The pressure created by the cell wall stops too much water entering and prevents cell lysis
Cells that are not turgid are flaccid (lacking in stiffness or strength)
Explain how a model shows osmosis in a cell
As water moves in by osmosis the vacuole fills up and presses out against the cell wall
Write a suitable plan to investigate into the effect of salt or sugar solutions on plant tissue
Prepare samples of potatoes (or other plant tissue)
Place in different concentrations of sugar or sodium chloride solution
Make measurements of mass and length of your samples before and after soaking them in solutions
Calculate the percentage change in mass of plant tissue
Active transport
Movement of a substance against a concentration gradient using energy
Why active transport is important for living organisms
Crucial for cell survival and rapid nutrient absorption by the cells
Why can’t root hair cells use diffusion to take up minerals from soil
Concentration of minerals is usually higher in root hair cells than in the soil around them
Why do plants need mineral ions
Healthy growth
What does active transport need to work
Energy from respiration to make it work
Example of how active transport happens in humans
Taking glucose from the gut
When is active transport used in the gut
When there is lower concenration of nutrients in the gut but a higher concentration of nutrients in the blood
What happens in there’s higher concentration of glucose and amino acids in the gut
They diffuse into the blood
When would a concentration gradient be the wrong way
When there’s a lower concentration of nutrients in the gut than there is blood
Urea
Waste product produced from breakdown of proteins
Where does urea diffuse from
Liver
What does how easy it is for an organism to exchange substances with its environment depend on
Organism’s surface area to volume ratio
The larger an organism is…
The smaller its surface area is compared to its volume
In single celled organisms how can gases and dissolved substances diffuse directly into (or out of) the cell across the cell membrane
They have large surface area compared to their volume
Why do multicellular organisms need some sort of exchange surface for efficient diffusion
Substances can diffuse from their outside surface to supply their entire volume.
Where does active transport take place
Root hair cells in plants
Small intestine
Kidneys
Nerve cells (neurons)
Differences between diffusion, osmosis and active transport
Active transport and osmosis always require a membrane, diffusion occurs with or without a membrane
Active transport requires energy, osmosis and diffusion don’t
Diffusion is high to low gradient, active transport is low to high and osmosis is high water potential to low water potential
How does active transport take place
Binding of molecules
ATP binding and release
Conformational change of transport protein
Release of molecule
Return to original shape
How a cell that carries out active transport is adapted to this function
High number of mitochondria
Abundance of transport proteins in membrane
Increased surface area of cell membrane
Removal of metabolic waste
Suggest improvements a representational model
that shows active transport
Show energy used
Direction of concentration gradients
Suggest limitations a representational model
that shows active transport
Oversimplification
Lack of context
Function of exchange surfaces
Allows water and other nutrients to enter the organism, and waste to be exchanged
How the effectiveness of exchange surfaces is increased
Large surface area
Short diffusion distance
Good blood supply
link ideas about diffusion to explain how the adaptations of exchange surfaces increases their effectiveness
Large surface area provides space for molecules to diffuse
Thin membranes reduces distance over which diffusion must occur
What ratio does a single celled organism have
Relatively large surface area to volume ratio
Use ideas about surface area to explain the shape of a leaf
Most leaves are broad and so have a large surface area
What do cells use diffusion for
To take in substances they need and get rid of waste products
When is oxygen and carbon dioxide transferred between cells and environment
During gas exchange
Where does gas exchange take place in the lungs
Alveoli
How are alveoli adapated for maximise diffusion
Enormous surface area
Thin walls
Moist lining
