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cell transport Flashcards

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Biology 101 flashcards
1
Q

define diffusion

A

the net movement of particles from a region of their higher concentration to a region of their lower concentration down a concentration gradient, as a result of their random movement

  • passive
  • will continue until molecules become evenly dispersed (equilibrium)
  • Small and non-polar (lipophilic) molecules will be able to freely diffuse across cell membranes (e.g. O2, CO2, glycerol)
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2
Q

describe the importance of diffusion of gases and solutes

give 4 eg. where diffusion of gases and solutes occurs in living organisms (plants and animals)

A

Life depends on the exchange of materials between cells and between cells and their surroundings

Diffusion has no energy cost, it is a passive process

  1. (A) Mammals: gas exchange surface formed of alveoli in lungs. Blood transports carbon dioxide and oxygen between the lungs and cells of the body. In the alveoli, oxygen diffuses in the opposite direction. Breathing constantly refreshes the air in the alveoli and blood and constantly removes oxy and brings in co2, o con. gradients always steep (many alveoli to give large SA for gas exchange)
    Oxygen moves through the membranes of structure in the lung called alveoli into the red blood cells and is carried to cells across the body for respiration. Carbon dioxide, the waste product of respiration, moves from the red blood cells into the lungs to be exhaled
  2. (A) Urea diffuses out of the liver cells into the blood plasma and is excreted by the kidneys
  3. (P) Carbon dioxide diffuse into the leaves through stomata (small “pores” on the leaves’ underside) Oxygen and water vapour also diffuse via them.
  4. (P) gas exchange inside leaves. Spongy mesophyll cells provide large SA for exchange of gases. There are air spaces between the cells in a plant and each cell exchanges gases with this air
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3
Q

describe the energy in diffusion

A

the energy for diffusion comes from the kinetic energy of random movement of molecules and ions

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4
Q

what factors influence diffusion

A

Surface area:

  • the larger the surface area the higher the number of particles that will be able to move in a given time (-> faster rate)
  • TB: some cell membranes are folded for bigger SA

Temperature:
- higher the temperature, the more the kinetic energy, more collisions and the faster the diffusion

Concentration gradient:

  • greater the difference in concentration -> faster the rate of diffusion
  • more particles are moving randomly down the gradient than against it
  • TB: cells use substances that diffuse as quickly as possible -> keep low conc. inside cytoplasm -> molecules keep diffusing into cell as cell is maintaining a steep conc. gradient

Distance:

  • less distance -> faster diffusion
  • if the diffusion distance is small, diffusion happens faster because the particles do not have as far to travel
  • TB: cell membranes -> thin

Molecular size
- larger particles are subjected to greater resistance within a fluid medium

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5
Q

cell membrane’s role

A

the cell membrane is a partially permeable membrane
plays a regulating role in controlling the substances allowed to pass in and out of cells

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6
Q

materials pass in and out of cells by:

A

diffusion
osmosis
active transport

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7
Q

give examples of substances cells require and remove

(+what can’t diffuse and why)

A

require: water, carbon dioxide, amino acids, lipids, glucose, oxygen, vitamins, mineral ions, hormones
removal: carbon dioxide, oxygen, urea, other metabolic wastes

molecules have to be small in order to move across (eg. oxygen, glucose, amino acids) but starch and proteins cannot

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8
Q

explain fick’s law

A

‘the rate of diffusion is proportional to both the surface area and concentration difference and is inversely proportional to the thickness of the membrane’.

rate of diffusion ∝ (surface area * concentration difference)/thickness of membrane

The rate of diffusion will double if:
1. surface area or concentration difference is doubled
or
2. thickness of the exchange membrane is halved.

All of the exchange surfaces consist of cell membranes which are very thin. This explains why diffusion is very fast across membranes.

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9
Q

define osmosis

A

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

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10
Q

explain the effects on plant tissues of immersing them in solutions of different concentrations

(+ name the different types

A

External solution is DILUTE -> HIGHER water potential

  • cell is TURGID
  • water will move INTO the cell and into the vacuole causing it to swell, resulting in tugor pressure (which is essential for keeping the leaves and stems of plants rigid)
  • solution is HYPOTONIC to the cell

External solution is CONCENTRATED -> LOW water potential

  • water will move OUT of the cell
  • the cell membrane peels away from the cell wall (called plasmolysis) and become plasmolysed
  • solution is HYPERTONIC to the cell

External solution of equal water potential -> cell is at EQUILIBRIUM

  • no net movement of water molecule (an equal number diffuse in and out of the cell by osmosis)
  • cytoplasm presses against cell wall
  • solution is ISOTONIC to cell
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11
Q

what is the difference between the roles played by the cell wall and the cell membrane in terms of osmosis

A

cell wall: fully permeable to all molecules, supports cell and prevents from bursting when gaining water by osmosis

cell membrane: partially permeable, water molecules pass through

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12
Q

what is the concentration gradient?

A

the difference between the concentration of molecules in two places
- molecules keep diffusing until they are spread evenly, when this happens the molecules keep moving, but there is no longer a difference in concentration -> diffusion stops

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13
Q

define passive movement

A

when the movement does not require energy

(cells do not need energy to move the molecules)

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14
Q

describe water as a solvent

A
  • sometimes called universal solvent
  • 75% of cytoplasm is water, main component of transport fluids (eg. blood, xylem sap, phloem sap)
  • everything transported in P and A has to dissolve in water
  • most chemical reactions in cells happen in water
  • water needed for digestion and excretion
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15
Q

what is a solution

A

a solution is made up of the solute and the solvent, the solute dissolves the solvent (solute isn’t always solid, liquids and cases can also be solutes as they dissolve in solvents)
soluble- smth that dissolves in a solvent

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16
Q

describe plasmolysis

A

plant cells in concentrated sugar/salt sol:
- water passes out by osmosis-> sap vacuole begins to shrink -> cell n/firm, becomes FLACCID -> more water leaves -> PLASMOLYSED

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17
Q

describe osmosis in animal cells

A

External solution is DILUTE -> HIGHER water potential

  • cell BURSTS (animal cells burst if they are placed into water as they have no cell wall to resist the increase in size)
  • water will move INTO the cell

External solution is CONCENTRATED -> LOW water potential

  • same as P
  • water will move OUT of the cell
  • the cell membrane peels away from the cell wall (called plasmolysis) and become plasmolysed
  • solution is HYPERTONIC to the cell

External solution of equal water potential -> cell is at EQUILIBRIUM

  • does not change size as the solution has the same water potential to inside the cell
  • this is how they are in the blood when surrounded by blood plasma
18
Q

describe facilitated diffusion

A

specialized proteins embedded in cell membrane to assist specific molecules to pass across the membrane (CARRIER/ TRANSPORT PROTEINS)

  1. molecule enters carrier protein
  2. carrier protein recognises the molecule and changes shape
  3. the molecules is now released on the other side of the membrane

PASSIVE- energy not required, molecules travel down concentration gradient

19
Q

define active transport

A

the movement of ions or molecules in or out of a cell through the cell membrane against a concentration gradient, using energy released during respiration

20
Q

what chemical is made from respiration, equation

A

ATMP released from respiration (like energised molecule)
respiration uses energy from chemically breaking down food molecules to replenish the energy contained in ATP
ATP -> ADP + Pi + Energy

21
Q

describe the process of active transport

A
  • the movement of ions or molecules in or out of a cell through the cell membrane against a concentration gradient (low conc to high conc)
  • requires cellular energy provided by respiration
  • cell membranes contain carrier proteins that provide means which by ions and molecules can move in/out of cell by active transp.
  1. molecule/ion combines will a carrier protein
  2. energy from respiration enables carrier protein to change its shape to carry the ion or molecule to inside of the membrane
  3. molecule/ion is released to inside of the membrane, carrier protein reverts to og shape
22
Q

describe active transport in

i) uptake of mineral ions by plants
ii) uptake of glucose by animals

A

i) when the concentration of an ion is greater inside the cell than in the soil water, the plant has to use active transport for ion uptake.
- plants take up ions such as nitrates and magnesium from the soil via root hair cells

ii) when the concentration of glucose in the blood is higher than in the gut lumen, epithelial cells lining the villi will need to use active transport to absorb glucose
(note: root hair cells + epithelial cells of villi are adapted for act. trans. by having many carrier proteins in their cell membranes and a high rate of respiration to provide energy)

23
Q

Active transport relies on _____ to ______
Any factor that _____ the rate of respiration will also affect __________
So a ____ of oxygen would ____ and ______

A

Active transport relies on respiration to take up ions or molecules against a conc. gradient

Any factor that affects the rate of respiration will also affect the rate of active transport

So a lack of oxygen would reduce respiration and active transport

24
Q

_____ can stop respiration so active transport will stop altogether

A

poisons such as cyanide

25
Q

increase of temperature will ____ the rate of respiration ___ act trans

A

++ temp -> ++ rate of respiration -> same effect on act trans

26
Q

Why is the diffusion of gases important

A

It allows for gas exchange in organisms to provide useful gases for processes like respiration and to remove waste gases

27
Q

Why is the diffusion of solutes important

A

It is useful for the uptake of solutes from the soil in plants

28
Q

What is a hypotonic solution

A

A solution that has higher water potential than the water potential of the cell

29
Q

What happens if you place an animal cell in a hypotonic solution

A

there is a net movement of water into the cell which causes the animal cell to burst (lyst)

30
Q

What happens if you place a plant cell in a hypotonic solution

A

there is a net movement of water into the cell which causes the plant cell to become turgid (it does not burst because of the strong cell wall)

31
Q

What happens if you place an animal cell in a hypertonic solution

A

There is a net movement of water out of the cell which causes the animal cell to shrink (crenate)

32
Q

What is a hypertonic solution

A

A solution that has lower water potential that the water potential of the cell

33
Q

What happens if you place a plant cell in a hypertonic solution

A

There is a net movement of water out of the cell which causes the plant cell to become plasmolysed

34
Q

What is an isotonic solution

A

A solution that has the same water potential as the water potential of the cell

35
Q

What happens if you put a cell in an isotonic solution

A

There is no net movement of water in or out of the cell

36
Q

How is a plant cell supported by water

A

The water creates turgor pressure which pushes the cell membrane against the inelastic cell wall

37
Q

give one use of active transport in humans

A
  • uptake of minerals and nutrients in the small intestine
  • reabsorption in the kidney
38
Q

give one use of active transport in plants

A

uptake of minerals into root hair cells

39
Q

how does active transport involve proteins

A

carrier proteins move substance from one side of the membrane to the other using energy

40
Q

why does oxygen diffuse into the blood from an alveolus in the lungs?

A

the oxygen concentration in the alveolus is greater than in the blood

41
Q

If visking tubing with a solution of starch, protease, protein, and simple sugars was inside, what would be present in the water surrounding it?

A

amino acids and simple sugars

bio (8 decks)

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