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Edexcel A Level Biology > Topic 2 > Flashcards

Topic 2 Flashcards

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1
Q

What is Fick’s law?

A

Rate of diffusion ∝ (area of diffusion surface x difference in concentration)/(thickness of diffusion surface)

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2
Q

When will the rate of diffusion double?

A

If the area of diffusion doubles
If the difference in concentration doubles
If the thickness of the diffusion surface halves

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3
Q

What do lungs allow to happen?

A

Rapid gaseous exchange

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4
Q

How have mammalian lungs adapted to increase the rate of gas exchange?

A

Lots of alveoli to increase the surface area
The alveolar epithethelium and capillary endothelium are one cell thick to decrease the distance of diffusion
Breathing refreshes the air in the alveoli to maintain a high concrentration gradient

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5
Q

What is the general structure of amino acids?

A

H2N-C(R)(H)-COOH

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6
Q

What does the R represent in the general structure?

A

The variable group that changes depending on the amino acid

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7
Q

How are polypeptides formed?

A

When two or more amino acids joined together in condensation reactions, with peptide bonds between the amino acid residues

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8
Q

What’s another name for polypeptides?

A

Proteins

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9
Q

Name the four levels of protein structure

A

Primary, secondary, tertiary, quaternary

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10
Q

Explain what the primary structure of proteins involves.

A

The primary structure is the flat sequence of amino acids in a polypeptide chain

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11
Q

Explain what the secondary structure of proteins involves.

A

Hydrogen bonds form between amino acid residues to make the chain coil into an alpha helix or into a beta pleated sheet, which makes the structure 3D

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12
Q

Explain what the tertiary structure of proteins involves.

A

The secondary structure is coiled and folded further. Hydrogen and ionic bonds form. If sulfur is present in any R groups, disulfide bridges form

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13
Q

When is the tertiary structure the final structure of a protein?

A

If the protein is made from a single polypeptide

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14
Q

Explain what the quanternary structure of proteins involves.

A

When several polypeptides are bonded together to form a protein

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15
Q

What are the different bonds that hold proteins together?

A

Peptide bonds in the primary structure
Hydrogen bonds in the secondary structure
Ionic bonds, hydrogen bonds, disulfide bridges, hydrophobic and hydrophilic interactions in the tertiary structure
All of the above in the quanternary structure

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16
Q

Explain what globular proteins are, giving an example

A

Round, compact structure made up of multiple polypeptide chains
Soluble because the hydrophilic parts of the proteins are on the outside and the hydrophobic parts are on the inside.
Haemoglobin is an example of a globular protein

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17
Q

Explain what fibrous proteins are, giving an example

A

Long insoluble proteins that are tightly coiled to form a rope like shape.
There are lots of bonds that hold the multiple chains together, making them strong- often supportive tissue
Collogen is an example of a fibrous protein

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18
Q

What are the main features of a cell membrane?

A

Phospholipid bilayer, protein molecules present, such as glycoproteins, glycolipids, and cholesterol

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19
Q

How is the the phospolipid bilayer arranged?

A

The hydrophilic ‘head’, the phosphate group, face towards the outside of the membrane, where the water is. The hydrophobic ‘tail’, two fatty acid groups, are inside the membrane, so as to get as far away from water as possible.

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20
Q

What does in mean that the cell membrane is partially permeable?

A

Small, uncharged molecules can diffuse through through gaps in the bilayer. Larger molecules and ions can only pass through channel proteins or carrier proteins

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21
Q

Define osmosis

A

The diffusion of free water molecules across a partially permeable membrane from an area of high concentration of water to an area of low concentration

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22
Q

What is facilitated diffusion?

A

Larger molecules and charged molecules can’t diffuse directly through the cell membrane. Instead, carrier proteins/channel proteins in the membrane allow these molecules to pass through the membrane

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23
Q

What do carrier proteins allow to diffuse across the cell membrane?

A

Large molecules, like amino acids

24
Q

What do channel proteins allow to diffuse across the cell membrane?

A

Charged particles

25
Q

Name three types of passive transport

A

Diffusion, osmosis, facilitated diffusion

26
Q

Define active transport

A

The movement of molecules/ions against their concentration gradient, using energy from the hydrolysis of ATP

27
Q

What is endocytosis?

A

Some molecules are too big to be taken into the cell by carrier proteins. Instead, the cell surrounds the substance with a section of the cell membrane. A vesicle, containing the ingested substance, is formed when the membrane pinches off. Energy from ATP used

28
Q

What is exocytosis?

A

There are molecules that need to be released from the cell. Vesicles with these substances pinch off the Golgi apparatus and move towards the cell membrane. The vesicle fuses with the membrane and release the substance out of the cell. ATP is the energy source

29
Q

Why do people with cystic fibrosis have stickier mucus than normal?

A

It contains less water than normal mucus

30
Q

What does this sticky mucus affect?

A

Respiratory system, digestive system, reproductive system

31
Q

How does CF affect the respiratory system?

A

Mucus builds up in the airways because cilia can’t move it. Therefore, the surface for gas exchange decreases, leading to breathing problems. People with CF are also prone to lung infections because microorganisms in the mucus can’t be removed.

32
Q

How does CF affect the digestive system?

A

The tube that connects the pancreas to the small intestine is blocked by the mucus, which prevents digestive enzymes reaching the small intestine. This reduces the ability to digest food. Cysts, caused by the mucus, grow in the pancreas, which inhibits the ability to produce digestive enzymes. All this leads to the absorption of nutrients being inhibited

33
Q

How does CF affect the reproductive systems?

A

Thick mucus in the reproductive systems cause fertility problems in men and women.
In some men, the tube connecting the testicles to penis is missing, and in others it’s blocked by thick mucus.
Women with CF have thickened cervical mucus, which prevents sperm reaching eggs.

34
Q

What are some of the treatments available for CF?

A
  • Antibiotics to kill bacteria in mucus
  • Physiotherapy
  • Digestive tablets
  • Gene therapy
  • Heart and lung transplant
35
Q

How is excess water removed from mucus in normal lungs?

A

1) Na+ is actively pumped out across basal membrane
2) Na+ diffuses through sodium channels in apical membranes
3) Cl- diffuses down electrical gradient
4) H2O is drawn out of cells due to increased NaCl in tissue fluid
5) Water is drawn out of mucus by osmosis

36
Q

How is water put back into mucus in normal lungs?

A

1) Cl- is pumped into lung cell across basal membrane
2) Cl- then diffuses out through open CFTR channels
3) Na+ diffuses down electrical gradient into mucus
4) Increased [NaCl] draws water out of cells by osmosis
5) Water is drawn back into the cell across basal membrane by osmosis

37
Q

How is mucus water level regulation affected in people with CF?

A

1) CFTR channel is absent or non-functional
2) The sodium channel in the apical membrane is permanently open
3) Water is continually removed from the mucus, making it sticky

38
Q

What are enzymes?

A

Biological catalysts, that catalyse metabolic reactions by providing alternative pathways with lower activation enthalpies.
Globular proteins, with charged R groups on the outside of the molecule

39
Q

Where do intracellular enzymes work?

A

They catalyse reactions inside cells

40
Q

Where do extracellular enzymes work?

A

They catalyse reactions outside cells

41
Q

Why are enzymes very specific?

A

Normally only one complementary substrate will fit into the active site

42
Q

What does this specificity lead to?

A

Enzymes only catalyse one reaction

43
Q

What determine the shape of the active site?

A

The tertiary structure of the enzyme

44
Q

Changes in pH and temperature lead to what in enzymes?

A

A change in the tertiary structure, which means the shape of the active site will be altered. This leads to the substrate not fitting, so the enzyme can’t function properly.

45
Q

What else might lead to a change in the tertiary structure of an enzyme?

A

A mutation in the gene responsible for the enzyme

46
Q

What is the basic structure of nucleotides, in both DNA and RNA?

A

Phosphate group attached to a pentose sugar by a phosphodiester bond. The sugar is attached to an organic nitrogenous base.

47
Q

What are the two types of organic nitrogenous bases?

A

Adenine and guanine are purines, which have two rings in their structure.
Thymine, cytosine, and uracil are pyrimidines, which have one ring in their structure.

48
Q

What is pentose sugar found in DNA?

A

Deoxyribose

49
Q

Pentose sugar in RNA?

A

Ribose

50
Q

How many hydrogen bonds form between adenine and thymine?

A

Two

51
Q

How many hydrogen bonds form between cytosine and guanine?

A

Three

52
Q

What do the hydrogen bonds between the two strands of DNA allow to happen?

A

They keep the strands together and are essential in creating the double helix.

53
Q

Nature of the genetic code?

A

The genetic code is a non-overlapping, degenerate triplet code

54
Q

Explain the term ‘non-overlapping’ with reference to the genome

A

Once the ribsome starts moving in one direction, it won’t go back in the other direction

55
Q

Explain the term ‘degenerate’ with reference to the genome

A

More than one triplet code codes for each amino acid

56
Q

Explain the term ‘triplet code’ with reference to the genome

A

Three bases make a triplet code, which then codes for an amino acid

Edexcel A Level Biology (8 decks)

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