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IP Secondary 3 Biology > Chapter 2 - Transport Across Membranes > Flashcards

Chapter 2 - Transport Across Membranes Flashcards

1
Q

What is diffusion?

A

The net movement of particles (ions or molecules) down a concentration gradient from a region of higher concentration to a region of lower concentration.

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2
Q

What is the relationship between concentration gradient and rate of diffusion?

A

The steeper the concentration gradient for a substance, the faster the rate of diffusion is for that substance

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3
Q

Why do particles diffuse?

A
  • The particles of fluids possess kinetic energy and are continually moving about
  • As their movement is random, the particles will diffuse down the concentration gradient and become evenly spaced out over time
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4
Q

A permeable membrane allows ________ to pass through it

A

both the solvent (water) and the solutes (the dissolved substances)

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5
Q

The cell membrane is ________

A

partially permeable

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6
Q

Oxygen and carbon dioxide move into and out of cells by ________

A

diffusion

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7
Q

What is facilitated diffusion?

A

The process of passive transport of molecules or ions passing through transmembrane/integral/transport proteins across a biological membrane.

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8
Q

Why is there a need for facilitated diffusion?

A

Polar or large molecules cannot easily pass through the hydrophobic region of the phospholipid bilayer by diffusion

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9
Q

How does a channel protein work?

A

Through a channel that can open or close

- transports ions/very small molecules

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10
Q

How does a carrier protein work?

A

By changing shape

  • molecule attaches to the binding site of the protein
  • protein changes configuration and releases molecule to the other side of the membrane
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11
Q

What is osmosis?

A

The net movement of water molecules from a region (solution) of less negative water potential to a region (solution) of more negative water potential, through a partially permeable membrane.

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12
Q

What is meant by “hypertonic”?

A

more negative water potential

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13
Q

What is meant by “hypotonic”?

A

less negative water potential

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14
Q

What is meant by “isotonic”?

A

same water potential

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15
Q

What happens to a plant cell in hypotonic solution?

A
  1. Cell sap has more negative water potential than that of the solution outside the cell.
  2. By osmosis, water enters the cell through the partially permeable cell membrane.
  3. Cell expands and becomes turgid.
  4. The vacuole increases in size and pushes the cytoplasm against the cell wall. The cell does not burst because it is protected by the inelastic cell wall.
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16
Q

How does the cell wall prevent the plant cell from bursting?

A

Cell wall is strong and relatively inelastic

- prevents over-expansion of cell by exerting an opposing pressure as water enters, preventing entry of more water

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17
Q

What happens to a plant cell in hypertonic solution?

A
  1. Cell sap has less negative water potential than that of the solution.
  2. By osmosis, water from the vacuole and cytoplasm leaves the cell through the partially permeable cell membrane.
  3. Cell decreases in size and becomes flaccid.
  4. The vacuole decreases in size and the cytoplasm and cell membrane shrinks away from the cell wall (plasmolysed).
    (Can be restored to its original state by placing it in water or in a solution with less negative water potential.)
18
Q

What happens to an animal cell in hypotonic solution?

A
  1. Cytoplasm has lower water potential than that of the solution.
  2. By osmosis, water enters the cell through the partially permeable cell membrane.
  3. Cell swells/expands and bursts (as it has no cell wall to protect it).
19
Q

What happens to an animal cell in hypertonic solution?

A
  1. Cytoplasm has higher water potential than that of the solution.
  2. By osmosis, water from the vacuole and cytoplasm leaves the cell through the partially permeable cell membrane.
  3. Cell shrinks and little spikes appear on the cell membrane (crenated).
  4. Cell will become dehydrated and eventually die.
20
Q

What happens to a plant/animal cell in isotonic solution?

A

Will not change in size or shape

21
Q

What is the importance of turgor in plant cells?

A

Maintains the shape of soft tissues in plants

  • Most leaves and young stems are able to remain firm and erect because of the turgor pressure within their cells
  • Plants wilts: due to high rate of evaporation of water from the cells and they lose their turgidity
  • Change in turgor of the guard cells cause the opening and closing of the stomata
22
Q

Why is it not advisable to add too much fertiliser around the roots of plants?

A
  • Soil solution will become very concentrated → cell sap of root hair cells has less negative water potential than soil.
  • Water will leave the roots by osmosis.
  • Inability of the roots to absorb water + continued evaporation of water from the leaves → plant will wilt.
23
Q

Example of osmosis: water entering root hair cell

A
  • Thin film of fluid surrounding each soil particle: dilute solution of mineral salts (less negative WP)
  • Water enters cell by osmosis
  • Water dilutes cell sap in fist cell (less negative WP compared to next cell)
  • Water moves from one cell to the next by osmosis
24
Q

Similarities between diffusion and osmosis

A
  • Passive processes (no energy required)

- Movement of substances down a concentration gradient

25
Q

Differences between diffusion and osmosis

A
  • Diffusion can be the movement of any substance whereas osmosis refers specifically to the movement of water molecules.
  • A partially permeable membrane is not required in diffusion but is required in osmosis.
26
Q

What is active transport?

A

The process in which energy (ATP molecules) is used to move particles against a concentration gradient (from a region of lower concentration to a region of higher concentration)

27
Q

Active transport occurs only in ________, energy used comes from ________

A

living cells

respiration

28
Q

Example of active transport (in plants)

A

Absorption of mineral salts by root hair cells

  • When concentration of ions/dissolved mineral salts in soil is lower than that in the cell sap
  • They are pumped into the cells
29
Q

Example of active transport (in humans)

A

Absorption of glucose and amino acids in the lumen by epithelial cells in the ileum (small intestine)

30
Q

Movement of glucose from ileum epithelial cells to blood capillaries in the villus is by ________

A

facilitated diffusion

31
Q

Similarities between facilitated diffusion and active transport

A
  • Transports solutes across cell membranes

- Involve transport proteins

32
Q

Differences between facilitated diffusion and active transport

A
  • Facilitated diffusion is the movement of substances from higher to lower concentration whereas active transport is from lower to higher concentration
  • Facilitated diffusion is a passive process (energy not required) whereas active transport is an active process (energy required)
33
Q

Surface area to volume ratio ________ with increasing cell size

A

decreases

34
Q

The greater the area of cell surface membrane per unit volume, the ________ the rate of diffusion of a substance for a given concentration gradient.

A

faster

35
Q

Surface area to volume ratio: why are cells so small?

A

Cells need to move waste materials and nutrients across their cell membrane quickly to stay alive

36
Q

Define “endocytosis”

A

A cellular process where cells absorb large molecules or ‘bulk materials’ from outside the cell by engulfing it via a membranous vesicle

37
Q

Examples of endocytosis

A
  • feeding by amoeba or paramecium

- phagocytosis and destruction of a bacterial cell by a white blood cell

38
Q

Why is endocytosis important to the cell?

A

Most molecules important to the cell cannot normally pass through the cell’s hydrophobic plasma membrane

39
Q

Define “exocytosis”

A

A cellular process where cells eject large molecules––waste products or cell products (such as enzymes and hormones)––from the interior of the cell via a membranous vesicle

40
Q

Examples of exocytosis

A
  • secretion of protein from cells

- secretion of waste material from cells

41
Q

Differences between endocytosis and exocytosis

A

In endocytosis, the cells absorb large molecules or ‘bulk materials’ from outside the cell to inside the cell whereas in exocytosis, the cells eject waste products or cell products from the interior of the cell to outside the cell

42
Q

Exocytosis is ________ in function to endocytosis but working in the ________ direction

A

similar

opposite

IP Secondary 3 Biology (8 decks)

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