Topic 1b - Transport in Cells Flashcards
(33 cards)
What is diffusion?
Diffusion is the spreading out of the particles of any substance in solution, or particles of a gas, resulting in a net movement from an area of higher concentration to an area of lower concentration.
How do small particles/ molecules move in and out of cells?
Very small particles/ molecules can diffuse through the cell membrane.
How do particles move in diffusion?
Freely.
What happens to big molecules?
Big molecules like starch and protein can’t fit through the membrane.
What are some examples of substances being transported in and out of cells by diffusion? (5)
- oxygen and carbon dioxide in gas exchange
- the waste product urea from cells into the blood plasma for excretion in the kidney
- water
- amino acids
- glucose
What are the factors that affect the rate of diffusion? (3)
- concentration gradient (difference in concentrations)
- temperature
- surface area (of the membrane)
How does the concentration gradient affect the rate of diffusion?
The bigger the concentration gradient (difference in concentrations), the faster the rate of diffusion because the net movement from one side is greater.
How does the temperature affect the rate of diffusion?
The higher the temperature, the faster the rate of diffusion because the particles have more energy and therefore move faster.
How does the surface area affect the rate of diffusion?
The larger the surface area (of the membrane), the faster the rate of diffusion because more particles can pass through at once.
Do single-celled organisms have a large SA:Vol? What does this allow?
A single-celled organism has a relatively large surface area to volume ratio. This allows sufficient transport of molecules into and out of the cell to meet the needs of the organism.
Do multicellular/larger organisms have a smaller or larger SA:Vol than smaller organisms?
- larger organisms = smaller SA:Vol
- smaller organisms = larger SA:Vol
How do you calculate an organisms Volume and Surface area?
Estimate the size of an organisms in the form of a block;
- Volume = length x width x height
- Area of one side = length x width
- Surface area = area of all the sides added together
What is the need for exchange surfaces and a transport system in multicellular organisms?
Multicellular organisms have a smaller SA:Vol, so not enough substances are able to diffuse from their outside surface to supply them with everything they need, therefore they need an exchange surface for diffusion.
How is the effectiveness of an exchange surface is increased? (4 adaptations)
- having a large surface area so lots of a substance can diffuse at once
- a membrane that is thin, to provide a short diffusion pathway
- (in animals) having an efficient blood supply, by having lots of blood vessels to get things in and out of the blood quickly
- (in animals, for gaseous exchange) being ventilated - air moves in and out
Where are villi found? What do they do? How are they adapted (3)?
- found in small intestine - mammals
- absorb food molecules (amino acids, glucose) into the blood stream
Adaptations;
- many villi increase the SA:Vol of the small intestine
- walls of the villi = 1 cell thick/single layer of surface cells - to ensure a short diffusion pathway
- a good blood supply maintains a steep concentration gradient
Where are alveoli found? What do they do? How are they adapted (3 adaptions)?
- found in the lungs - mammals
- the alveoli carry out gas exchange (oxygen absorbed into bloodstream + carbon dioxide released)
adaptations;
- millions of alveoli in each lung, providing large SA for diffusion
- alveoli has a moist surface for gases to dissolve
- a large capillary network ensures that blood constantly moves oxygen away from the lungs - maintaining a steep concentration gradient
What do the gills of a fish do? How are they adapted? (3 adaptations)
- the gills carry out gas exchange under the water (oxygen = absorbed into the blood + carbon dioxide is released)
adaptations;
- many gill filaments provide a large SA for diffusion (each gill filament has folds in the surface, lamellae, to further increase the SA)
- the membrane of the gill filaments = 1 cell thick, providing a short diffusion pathway
- flow of blood = in opposite direction to the flow of water across the gill filaments, so there is a steep concentration gradient
What do the leaves do - in terms of diffusion? How are they adapted (3)?
- leaves carry out gas exchange (carbon dioxide is taken into the leaf + oxygen is released)
adaptations
- broad, flat shape provides a large SA for diffusion
- leaf = thin, providing a short diffusion pathway
- many air spaces to allow gases to easily diffuse through the leaf, maintaining a steep concentration gradient
What is osmosis?
Water may move across cell membranes via osmosis. Osmosis is the diffusion of water from a dilute solution (region of higher water concentration) to a concentrated solution (region of low water concentration) through a partially permeable membrane.
What is osmosis a type of and what does it do?
Diffusion - passive movement of water molecules down the concentration gradient.
Which side of the membrane does water go during osmosis?
The water molecules pass through to both sides of the membrane during osmosis, but because of the concentration gradient there is a net movement from high to low.
What does Hypertonic mean? And what does this cause the cell to look like in animals and plants?
- Hypertonic = The solution is concentrated/contains very little water.
- Shrivelled in animal cells
- Plasmolyzed in plant cells
What does Hypotonic mean? And what does this cause the cell to look like in animals and plants?
- Hypotonic = The solution is dilute/contains a lot of water.
- Lysed in animal cells
- Turgid (normal) in plant cells
What does Isotonic mean? And what does this cause the cell to look like in animals and plants?
- Isotonic = There is no difference in concentration between the solute and water, and the movement of water remains constant.
- Normal in animal cells
- Flaccid in plant cells
