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A-Level Biology > Organisms exchange substances with their environment > Flashcards

Organisms exchange substances with their environment Flashcards

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1
Q

What are the three disaccharides in the spec. to do with digestion

A

• Maltose
• Sucrose
• Lactose

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2
Q

What enzymes hydrolyse disaccharides

A

Disaccharidases

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3
Q

What disaccharidase hydrolyses maltose

A

Maltase

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4
Q

What disaccharidase hydrolyses sucrose

A

Sucrase

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5
Q

What disaccharidase hydrolyses lactose

A

Lactase

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6
Q

What are the products of the hydrolysis of maltose

A

Glucose + Glucose

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7
Q

What are the products of the hydrolysis of sucrose

A

Glucose + Fructose

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8
Q

What are the products of the hydrolysis of lactose

A

Glucose + Galactose

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9
Q

Why’s there no carbohydrate digestion in the stomach (2)

A
  1. Too acidic for salivary amylase
  2. Stomach enzymes only digest proteins
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10
Q

What are membrane bound disaccharidases

A

Enzymes attached to the cell surface membrane of epithelial cells lining the ileum

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11
Q

How is fructose absorbed

A

Via facilitated diffusion through a transport protein

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12
Q

How are glucose and galactose absorbed (the two G’s)

A

By active transport with Na+ ions via a co-transporter protein

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13
Q

What is digestion of lipids

A

Hydrolysis of ester bonds

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14
Q

What are triglycerides broken down into

A

A monoglyceride and two fatty acids

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15
Q

How are fatty acids absorbed into the blood

A

By simple diffusion

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16
Q

What enzyme hydrolyses lipids

A

Lipase

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17
Q

Where are lipase enzymes produced

A

The pancreas where they’re secreted into the small intestine in pancreatic juice

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18
Q

Where are bile salts produced

A

The liver

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19
Q

What do bile salts do

A

Lower surface tension between lipids and water so large drops of lipid split into smaller ones (Emulsification)

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20
Q

What’s emulsification

A

Bile salts lower surface tension between lipids and water so large drops of lipid split into smaller ones

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21
Q

What does emulsification do

A

Increases surface area for lipase enzymes to act on

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22
Q

How are micelles formed

A

The products of lipid digestion (monoglyceride + fatty acids) stick to bile salts to form micelles

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23
Q

What’s a micelle

A

the products of lipase digestion that remain in association with the bile salts to form structures

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24
Q

What do micelles do

A

• Help move monoglycerides and fatty acids to the epithelial cells
• constantly break up and reform so they can release their monoglycerides and fatty acid, allowing them to be absorbed

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25
Q

What is protein digestion

A

Hydrolysis of peptide bonds

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26
Q

What enzyme breaks down protein

A

Protease

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27
Q

What are the three types of protease

A
  1. Endopeptidase
  2. Exopeptidase
  3. Membrane bound dipeptidase
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28
Q

What do endopeptidases do

A

Hydrolyse peptide bonds within a protein

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29
Q

What do exopeptidases do

A

Hydrolyse bonds one bond from the end of a protein

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30
Q

What do membrane bound dipeptidases do

A

Hydrolyse bonds in dipeptides while attached to the cell surface membrane for epithelial cells in the ileum

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31
Q

What’s the product of protein digestion

A

Amino acids

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32
Q

How are amino acids absorbed

A

(Similarly to glucose and galactose) By co-transport through an Na+ co-transporter protein to the lumen

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33
Q

Why must heat be exchanged by organisms with their environment

A

To maintain a constant temperature

34
Q

What happens if waste products build up

A

Cells die

35
Q

Gaseous exchange definition

A

Diffusion of oxygen from the air in the alveoli into the blood and of carbon dioxide from the blood into the air in the alveoli

36
Q

Adhesion definition

A

• Attraction of molecules of one kind for molecules of a different kind
• It can be quite strong for water, especially with other molecules bearing positive or negative charges

37
Q

Cohesion definition

A

• Attraction between molecules of the same type

• How water molecules form hydrogen bonds between one another and hence tend to stick together

38
Q

What’s the cohesion-tension theory

A

The main factor that’s responsible for the movement of water up the xylem, from the roots to the leaves.
Transpiration pull puts the xylem under tension (there is negative pressure within the xylem) and because of the cohesive nature of water (due to hydrogen bonds between water molecules) there is a continuous stream of water being pulled across the mesophyll cells and up the xylem

39
Q

What’s a companion cell

A

Since the sieve tube element lacks organelles, the companion cell controls the movement of solutes and provides ATP for active transport in the sieve tube element.

40
Q

What connect the sieve tube element and the companion cell

A

Strands of cytoplasm called plasmodesmata

41
Q

Diffusion definition

A

The movement of molecules or ions from a region where they’re in high concentration to one where their concentration is lower

42
Q

What’s a guard cell

A

One of a pair of cells that surround a stoma in plant leaves and controls it’s opening and closing

43
Q

What’s a hydrogen bond

A

Chemical bond formed between the positive charge of a hydrogen atom and the negative charge on another atom of an adjacent molecule

44
Q

Hydrolysis definition

A

The breaking down of larger molecules into smaller ones by the addition of water molecules

45
Q

What’s an ion

A

An atom or group of atoms that has lost or gained one or more electrons

46
Q

What’s an ion channel

A

A passage across a cell surface membrane made up of a protein that spans the membrane and opens and closes to allow ions to pass in and out of the cell

47
Q

Isotonic definition

A

Solutions that possess the same concentration of solutes and therefore have the same water potential

48
Q

What’s the mass-flow theory

A

• The bulk movement of a substance through a given channel or area in a specified time.
• Sucrose is transferred into sieve elements from photosynthesising tissue so there can be mass flow of sucrose solution down a hydrostatic gradient in sieve tubes
• caused by active transport (of sucrose into sieve tubes at the source and out of sieve tubes at the sink)
• and osmosis (movement of water into sieve tubes near sources and out of sieve tubes near sinks)

49
Q

What’s mesophyll

A

Tissue found between the two layers of epidermis in plant leaves comprising an upper layer of palisade cells and a lower layer of spongey cells

50
Q

Metabolism definition

A

All the chemical processes that take place in living organisms

51
Q

What are Microvilli

A

Tiny, finger-like projections from the cell surface membrane of some animals

52
Q

What are middle lamella

A

Layer made up of pectins and other substances found between the walls of adjacent plant cells

53
Q

What’s mitosis

A

The type of nuclear division in which the daughter cells have the same number of chromosomes as the parent cell

54
Q

What’s a monomer

A

One of the many small molecules that combine to form a polymer

55
Q

Osmosis definition

A

The movement of water from a region of high water potential to a region of lower water potential through a partially permeable membrane

56
Q

What are palisade cells

A

Long, narrow cells packed with chloroplasts that are found in the upper region of a leaf and which carry out photosynthesis

57
Q

What’s the phloem

A

Plant tissue that transports the products of photosynthesis from leaves to the rest of the plant

58
Q

What’s a potometer

A

A piece of apparatus which measures the rate of water loss in a plant

59
Q

What would you use to measure the rate of water loss in a plant

A

A potometer

60
Q

What’s a protoplast

A

The living portion of a plant cell (i.e. the nucleus and cytoplasm along with the organelles it contains)

61
Q

What’s ringing

A

• An experiment when a section of outer layers (protective layer and phloem) is removed around the complete circumference of a woody stem while it’s still attached to the rest of the plant.
• This results in the region of the stem immediately above the missing ring of tissue swelling because the sugars of the phloem accumulate above the ring and it leads to tissues dying below the ring because of the interruption of flow of sugars to this region.

62
Q

What does ringing show

A

That the phloem is responsible for translocating sugars

63
Q

What’s a sieve tube element

A

Living, tubular cells that are connected end to end. The cell walls have perforations in them to make sieve plates.
The cytoplasm’s present but in small amounts and in the layer next to the cell wall.
It lacks a nucleus and most organelles so there’s more space for solutes to move.
The cell walls are made of cellulose so solutes can move laterally as well as vertically.
Next to each sieve tube is a companion cell

64
Q

What’s a stoma (stomata)

A

A pore, mostly in the lower epidermis of a leaf through which gasses diffuse in and out of the leaf

65
Q

What’s a tracer

A

• Radioactive isotopes can be used to trace the movement of substances in plants.
• ^14CO2 is used so plants incorporate this isotope into the sugars produced during photosynthesis.
• These radioactive sugars can then be traced as they move within the plant using autoradiography

66
Q

How can radioactive sugars be traced moving through a plant

A

Autoradiography

67
Q

What radioactive isotope is used to trace the movement of substances in plants

A

^14 CO2

68
Q

What do tracers show

A

Sugars are found where phloem tissue is in the stem

69
Q

What’s translocation

A

The process by which organic molecules and some mineral ions are transported from one part of a plant to another

70
Q

What’s transpiration

A

The main force that pulls water through the xylem vessels in the stem of a plant is the evaporation of water from leaves through stomata

71
Q

What’s transpiration pull

A

How a column of water is pulled up the xylem as a result of transpiration

72
Q

What’s water potential

A

The pressure created by water molecules.
The measure of the extent to which a solution gives out water

73
Q

What are xylem vessels

A

Dead, hollow, elongated tubes with lignified side walls and no end walls, that transport water in most plants

74
Q

Outline the mass flow hypothesis

A
  1. Companion cells actively transport hydrogen ions (H+) into the source cell
  2. This creates a concentration gradient of hydrogen ions between the source and companion cell
  3. H+ wants to diffuse back due to the new concentration gradient, sucrose is co-transported into the sieve tube with H+ through special transport proteins that require a sucrose molecule by companion cells
  4. Water potential in the sieve tubes’ lowered do water moves from the xylem into the sieve tube by osmosis
  5. Increased hydrostatic pressure
  6. Mass flow of substances (sucrose) to respiring cells in the sink
  7. Facilitated diffusion of sucrose from the phloem into the sink cells
  8. Water potential at the phloem increases, so water moves by osmosis back into the xylem
75
Q

What evidence supports the fact that saps under positive pressure in the phloem within the mass flow hypothesis

A

When sieve tubes are cut, sap’s released

76
Q

What does sap being released when sieve tubes are cut suggest

A

saps under positive pressure in the phloem within the mass flow hypothesis

77
Q

What evidence supports the fact there’s a pressure gradient in the phloem within the mass flow hypothesis

A

• Aphids tap into the phloem to consume sap- the high pressure forces it through their digestive system resulting in the excretion of honeydew.
• Honeydew tends to flow faster out of aphids higher up the plant near leaves than lower down the stem.

78
Q

What evidence supports the presence of sources and sinks within the mass flow hypothesis

A

Sucrose concentrations higher in leaves than roots

79
Q

What does the fact sucrose concentrations higher in leaves than roots support in terms of the mass flow hypothesis

A

The presence of sources and sinks

80
Q

4 pieces of evidence supporting the mass flow theory

A
  1. Increases in sucrose in leaves are followed by increases in sucrose in the phloem
  2. Downward flow in the phloem occurs in daylight when photosynthesis is occurring but not at night; due to greater respiration at night and lack of photosynthesis that would mean there would no longer be a pressure gradient
  3. Preventing ATP production stops translocation but not water movement. A lack of ATP for active transport in companion cells would kill them which would prevent mass flow
  4. Ringing
81
Q

2 pieces of evidence against the mass flow hypothesis

A
  1. Sugar travels to many different sinks and doesn’t travel first or faster to the one with the highest water potential which it should according to the mass flow hypothesis
  2. The end plates of the sieve tubes would create a barrier to mass flow, or slow it down, so why are they present?

A-Level Biology (9 decks)

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