[Part 2]- B2-cell division 🧫 Flashcards
Explain why single-celled organisms can rely on diffusion to transport molecules in, and out of their cell.
Hint: not diffusion
- single-celled organisms [such as amoeba] can rely on diffusion to transport molecules in and out of their cell, because they have a large surface area to volume ratio.
What happens to the surface area, to volume ratio as organisms get larger? [1]
- As organisms get larger, the surface area: volume ratio falls sharply.
What happens to the surface area, to volume ratio as organisms get larger? Explain if this is a problem or not [4]
Hint: can diffuse into the cells
- as organisms get larger, the surface area: volume ratio falls sharply.
- this is a huge problem for multicellular organisms, because their surface area is not large for their volume.
- therefore cells on the surface can’t get enough oxygen simply by diffusion, and not enough oxygen can diffuse into the cells, in the centre of the organism.
- This is because they’re too far away from the surface.
Explain how the gills in fish, are adapted for exchanging materials. 🐟 [4]
Hint: deoxygenated blood passes
- with fish, the oxygen-rich water passes into the mouth. It then flows over gills, where the oxygen is transported into the bloodstream.
- Their gills are made up of stacks of thin filament, where gases pass in and out of the blood.
- their gills have a large surface area to increase diffusion, and their gills also have a network of capillaries- to provide a good blood supply
- Deoxygenated blood then passes into the filament.
- oxygen diffuses from the water, into the blood + oxygenated blood returns to the body.
What are the 3 adaptations of a fish’s filaments? [3] 🐟
Hint: take the oxygenated blood away
- filaments give the gills a massive [large] surface area- to increase diffusion
- fish filaments also have a thin membrane- to a short diffusion pathway.
- fish’s filaments also have an efficient and good blood supply to take the oxygenated blood away- ensuring the concentration gradient is always high. [by having a network of capillaries]
Explain the four ways how the effectiveness of an exchange surface is increased [4]
- having a large surface area
- a thin membrane= provides a short diffusion path
- [in animals] - having an efficient blood supply
- [in animals, for gaseous exchange]- being ventilated.
Explain how the lungs in mammals, are adapted for exchanging materials.
- the role of the lungs is to transfer oxygen to the blood, and to also remove waste carbon dioxide from it.
- To do this, lungs contain millions of alveoli where gaseous exchange takes place.
- to maximise the diffusion of O2 and CO2, alveoli have: a large surface area, a moist lining for dissolving gases, network of capillaries to provide a good blood supply and very thin walls [because the membrane of the alveoli is only one cell thick- proving a short diffusion pathway]
Explain how the small intestine in mammals, are adapted for exchanging materials. [5]
- in mammals, the small intestine is covered in millions of villi, which increase the surface area, so digested food is absorbed much quicker into the blood.
- villi have: a thin wall [that is only one cell thick], a good blood supply- which assists quick absorption, a large surface area due to folding and a network of capillaries
How are roots and leaves in plants, adapted for exchanging materials? [3]
Hint: underneath of a leaf
- carbon dioxide diffuses into the air species, within the leaf—-> diffuses into the cell [where photosynthesis happens]
- the underneath of a leaf is an exchange surface- as it is covered in stomata, where carbon dioxide diffuses in through.
- oxygen and water vapour diffuse out through the stomata
Explain other ways how roots and leaves in plants, are adapted for exchanging materials. [4]
Hint: 🤐, 🥿, 🧱
- the size of the stomata is controlled by guard cells. Guard cells close, if the plant is losing water faster then it’s replaced [by the roots]. Without guard cells= plant wilts.
- a leaf has a flattened shape= increases the area of exchange surface= more efficient
- walls of the cells inside the leaf have air spaces inside the leaf= increases area of surface= more chance for CO2 to get into the cells.
What is ‘osmosis’ ?
- Osmosis, is the diffusion of water from a dilute solution [high] to a concentrated solution [low], through a partially permeable membrane.
What do dilute solutions contain 🆚 a concentrated solution ?
- dilute solutions contain a high concentration of water
- ; concentrated solutions contain a low concentration of water.
How can osmosis have major affects on cells?
- the cytoplasm of cells is a relatively concentrated solution. It contains a low concentration of water; if the cell is placed in water osmosis will take place:
- water will move by osmosis, from outside the cell, to inside the cell.
- With an animal cell, water moving in, will cause the cell to expand + it could burst.
- But if we place a cell in a concentrated solution, water moves out of the cell by osmosis= the cell will shrink
How can osmosis affect plant cells?
- If a plant cell is placed in water, water moves into the cell by osmosis + the cell will expand; the cell wall prevents the plant cell from bursting.
- Instead, it becomes turgid [becomes swollen]
- But If we place a plant cell into a concentrated solution, water moves out of the plant cell by osmosis= causing the cell to become flaccid [shrink]
How can osmosis affect plant cells?
- If a plant cell is placed in water, water moves into the cell by osmosis + the cell will expand; the cell wall prevents the plant cell from bursting.
- Instead, it becomes turgid [becomes swollen]
- But If we place a plant cell into a concentrated solution, water moves out of the plant cell by osmosis= causing the cell to become flaccid [shrink]
