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Biology Edexcel Sophie > Topic 2 Transport And Exchange > Flashcards

Topic 2 Transport And Exchange Flashcards

1
Q

What is gas exchange?

A

The process by which organisms exchange gases with their environment, involving diffusion.

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2
Q

Define diffusion.

A

The net movement of particles from an area of higher concentration to an area of lower concentration.

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3
Q

What is the concentration gradient?

A

The path from an area of higher concentration to an area of lower concentration.

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4
Q

Is diffusion an active or passive process?

A

Passive process — no energy is needed.

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5
Q

What two characteristics do most gas exchange surfaces have in common?

A
  • Large surface area to volume ratio
  • Thin surface (often one layer of epithelial cells)
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6
Q

What is Fick’s Law?

A

A law that relates the rate of diffusion to the concentration gradient, surface area, and thickness of the exchange surface.

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7
Q

According to Fick’s Law, what happens if the surface area doubles?

A

The rate of diffusion will double.

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8
Q

What happens to the rate of diffusion if the thickness of the surface halves?

A

The rate of diffusion will double.

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9
Q

What effect does temperature have on the rate of diffusion?

A

The rate of diffusion increases with temperature due to increased kinetic energy of molecules.

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10
Q

Describe how surface area to volume ratios affect gas exchange.

A

Larger objects have smaller surface area to volume ratios, resulting in slower rates of exchange.

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11
Q

What is the surface area to volume ratio of a small cube with a surface area of 24 cm² and volume of 8 cm³?

A

3:1

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12
Q

What is the permeability constant for oxygen across the alveolar epithelium?

A

0.012 s⁻¹

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13
Q

Calculate the rate of diffusion of oxygen across the alveolar epithelium given the concentrations.

A

3.7 × 10⁻¹⁸ mol um⁻² s⁻¹

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14
Q

What is the gas exchange surface in mammals?

A

The alveolar epithelium in the lungs.

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15
Q

How does oxygen move during gas exchange in the lungs?

A

Oxygen diffuses out of the alveoli, across the alveolar epithelium and into the blood.

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16
Q

What features of the mammalian lungs increase the rate of gas exchange?

A
  • Lots of alveoli (large surface area)
  • Alveolar epithelium and capillary endothelium are one cell thick
  • Good blood supply from capillaries
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17
Q

True or False: Breathing in and out helps maintain concentration gradients in the alveoli.

A

True

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18
Q

Fill in the blank: The smaller the surface area to volume ratio, the _______ the rate of exchange.

A

slower

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19
Q

What are the main components of cell membranes?

A

Lipids, proteins, carbohydrates

Mainly phospholipids, which are a type of lipid with a phosphate group attached.

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20
Q

What does the fluid mosaic model describe?

A

The arrangement of molecules in the cell membrane

Proposed in 1972, it illustrates the dynamic nature of the membrane.

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21
Q

What is the structure of phospholipid molecules?

A

A hydrophilic head and two hydrophobic fatty acid tails

The head attracts water, while the tails repel water.

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22
Q

What is the arrangement of phospholipids in the cell membrane?

A

Phospholipids form a bilayer

The hydrophilic heads face outward, and the hydrophobic tails face inward.

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23
Q

What role does cholesterol play in the cell membrane?

A

It increases rigidity at higher temperatures and fluidity at lower temperatures

Cholesterol fits between phospholipids, influencing membrane properties.

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24
Q

What are glycoproteins?

A

Proteins with attached polysaccharide chains

They are involved in cell recognition and signaling.

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25
Q

What are glycolipids?

A

Lipids with attached polysaccharide chains

They also contribute to cell recognition and stability.

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26
Q

What is the permeability of the cell membrane?

A

Partially permeable

Small molecules can pass through, while larger molecules require specific proteins.

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27
Q

What is osmosis?

A

The diffusion of free water molecules across a partially permeable membrane

It occurs from an area of higher concentration to lower concentration of water.

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28
Q

Fill in the blank: Osmosis is the diffusion of __________ molecules across a partially permeable membrane.

A

Water

This process is crucial for maintaining cell turgor and homeostasis.

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29
Q

True or False: The cell membrane is mainly composed of glycolipids.

A

False

The main components are lipids, proteins, and carbohydrates.

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30
Q

What did improved electron microscopy reveal about cell membranes?

A

They show a bilayer of phospholipids with proteins randomly distributed

This contradicted earlier beliefs of a continuous protein layer.

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31
Q

Describe an experiment that proved the fluidity of cell membranes.

A

Fusing a mouse cell with a human cell showed intermixed membrane proteins

This mixing indicated that the membrane is fluid.

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32
Q

What happens to water molecules during osmosis?

A

They diffuse both ways through the membrane, but net movement is to the lower concentration side

This process is essential for cell volume regulation.

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33
Q

What is the significance of the term ‘fluid’ in the fluid mosaic model?

A

It indicates that the components of the membrane can move laterally within the layer

This fluidity is crucial for membrane function and flexibility.

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34
Q

What does ‘partially permeable’ mean in terms of cell membranes?

A

It allows some substances to pass while restricting others

This property is vital for maintaining cellular environments.

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35
Q

What is the net movement of water molecules in osmosis?

A

From an area of higher concentration of water molecules to an area of lower concentration

The presence of solutes affects the concentration of water.

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36
Q

What did scientists believe about cell membranes before the 1970s?

A

They thought cell membranes were composed of a phospholipid layer between two continuous layers of proteins

This was based on earlier electron microscope images.

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37
Q

What is facilitated diffusion?

A

A passive transport process that uses carrier proteins and channel proteins to move molecules down a concentration gradient

Facilitated diffusion is used for larger molecules and charged particles that cannot diffuse directly through the phospholipid bilayer.

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38
Q

How do carrier proteins function in facilitated diffusion?

A

They move large molecules into or out of the cell by changing shape after binding the molecule

This process releases the molecule on the opposite side of the membrane.

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39
Q

What is the main difference between facilitated diffusion and active transport?

A

Active transport moves substances against a concentration gradient and uses energy, while facilitated diffusion does not

Active transport involves carrier proteins and requires ATP.

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40
Q

What energy source is used in active transport?

A

ATP

ATP is produced by respiration and acts as an immediate source of energy in the cell.

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41
Q

Define endocytosis.

A

The process by which a cell surrounds a substance with its cell membrane to take it in, forming a vesicle

This is used for large molecules that cannot enter through carrier proteins.

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42
Q

What is exocytosis?

A

The process of releasing substances from a cell by vesicles fusing with the cell membrane

This process is used to secrete substances like enzymes and hormones.

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43
Q

What substances can be taken in by endocytosis?

A

Proteins, lipids, carbohydrates, microorganisms, and dead cells

White blood cells, called phagocytes, use endocytosis to destroy microorganisms.

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44
Q

What occurs during the process of exocytosis?

A

Vesicles containing substances pinch off from the Golgi apparatus, move to the cell membrane, and release their contents outside the cell

Some substances are inserted directly into the cell membrane instead of being released.

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45
Q

True or False: Facilitated diffusion requires energy.

A

False

Facilitated diffusion is a passive process.

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46
Q

Fill in the blank: Active transport moves substances _______ a concentration gradient.

A

against

This process requires energy to move molecules from low to high concentration.

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47
Q

What is the role of membrane proteins in facilitated diffusion?

A

They facilitate the movement of specific molecules across the cell membrane by providing channels or carriers

Different proteins are specific to different molecules.

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48
Q

Explain the difference between endocytosis and exocytosis.

A

Endocytosis involves the intake of substances into the cell, while exocytosis involves the release of substances from the cell

Both processes utilize ATP for energy.

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49
Q

What is the permeability of the cell membrane?

A

The cell membrane is partially permeable, allowing some molecules to pass through while restricting others.

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50
Q

How can membrane permeability be investigated in the lab?

A

By performing an experiment using beetroot to measure pigment leakage under different conditions.

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51
Q

What factors affect the permeability of cell membranes?

A
  • Temperature
  • Alcohol concentration
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52
Q

What is the effect of temperature on beetroot membrane permeability?

A

Higher temperatures increase the permeability of the membrane.

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53
Q

What happens to beetroot cells at temperatures below 0 °C?

A

Phospholipids are rigid, and channel proteins deform, increasing membrane permeability.

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54
Q

What occurs in beetroot cells at temperatures between 0 °C and 45 °C?

A

Phospholipids move more freely, leading to increased membrane permeability.

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55
Q

What happens to the phospholipid bilayer at temperatures above 45 °C?

A

The bilayer begins to melt, increasing permeability and causing channel proteins to deform.

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56
Q

What is a colorimeter used for?

A

To measure the absorbance of a colored solution, indicating the amount of pigment released.

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57
Q

Describe the procedure for measuring the absorbance of beetroot solution.

A
  • Calibrate colorimeter with pure water
  • Transfer beetroot solution to a cuvette
  • Record absorbance
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58
Q

What effect does increasing alcohol concentration have on membrane permeability?

A

Increases permeability by dissolving lipids in the cell membrane.

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59
Q

Fill in the blank: The higher the absorbance reading, the _______ light is passing through the solution.

A

less

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60
Q

True or False: Ice crystals can form in beetroot cells at low temperatures, potentially increasing permeability when thawed.

A

True

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61
Q

What are the temperature ranges associated with changes in membrane permeability?

A
  • Below 0 °C: Rigid membrane
  • 0 °C to 45 °C: Increased fluidity
  • Above 45 °C: Melting of the bilayer
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62
Q

What is the significance of the colored pigment in beetroot cells during permeability experiments?

A

It serves as an indicator of membrane permeability, as it leaks out when permeability increases.

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63
Q

What is the relationship between alcohol concentration and membrane permeability based on the experiment?

A

As alcohol concentration increases, membrane permeability also increases.

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64
Q

What does a higher absorbance reading indicate about beetroot membrane permeability?

A

It indicates that more pigment has been released, meaning higher permeability.

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65
Q

What are the monomers of proteins?

A

Amino acids

Amino acids are the building blocks of proteins.

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66
Q

What is formed when two amino acids join together?

A

Dipeptide

A dipeptide is the simplest form of a protein chain.

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67
Q

What is a polypeptide?

A

More than two amino acids joined together

Polypeptides are longer chains that make up proteins.

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68
Q

What is the primary structure of a protein?

A

The sequence of amino acids in the polypeptide chain

The primary structure is crucial for determining a protein’s function.

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69
Q

What type of bonds hold the primary structure of a protein together?

A

Peptide bonds

Peptide bonds are covalent bonds formed between amino acids.

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70
Q

Describe the secondary structure of a protein.

A

Coiling into an alpha helix or folding into a beta pleated sheet

Secondary structures are stabilized by hydrogen bonds.

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71
Q

What interactions contribute to the tertiary structure of a protein?

A

Hydrogen bonds, ionic bonds, disulfide bonds, hydrophobic and hydrophilic interactions

These interactions determine the protein’s final 3D shape.

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72
Q

What is the quaternary structure of a protein?

A

The way multiple polypeptide chains are assembled together

Examples include proteins like hemoglobin and collagen.

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73
Q

What is unique about glycine among amino acids?

A

It doesn’t have carbon in its side group

Glycine is the simplest amino acid.

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74
Q

What is the role of disulfide bonds in proteins?

A

They form between cysteine molecules, stabilizing protein structure

Disulfide bonds are important for maintaining the tertiary and quaternary structures.

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75
Q

What defines globular proteins?

A

Round, compact structure made of multiple polypeptide chains

Globular proteins are typically soluble and functional in biological systems.

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76
Q

What is an example of a globular protein?

A

Hemoglobin

Hemoglobin carries oxygen in the blood and is soluble.

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77
Q

How are fibrous proteins characterized?

A

Long, insoluble polypeptide chains that form a rope shape

Fibrous proteins are often structural and strong.

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78
Q

What is an example of a fibrous protein?

A

Collagen

Collagen provides strength and structure to connective tissues.

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79
Q

Fill in the blank: Amino acids are linked together by _______ to form polypeptides.

A

Condensation reactions

During this process, a molecule of water is released.

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80
Q

True or False: The 3D structure of a protein is independent of its amino acid sequence.

A

False

The amino acid sequence dictates the folding and final structure.

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81
Q

What happens to a protein’s structure when it is heated to a high temperature?

A

Its ionic and hydrogen bonds break, leading to denaturation

Denaturation results in loss of function.

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82
Q

What are the four types of bonds that determine the 3D structure of a protein?

A

Peptide bonds, hydrogen bonds, ionic bonds, disulfide bonds

These bonds play critical roles in maintaining protein stability.

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83
Q

What are enzymes?

A

Biological catalysts that speed up chemical reactions

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84
Q

What is a catalyst?

A

A substance that speeds up a chemical reaction without being used up

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85
Q

What types of reactions do enzymes catalyse?

A

Metabolic reactions at both cellular and organismal levels

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86
Q

Where can enzymes be located?

A

Intracellular (inside cells) or extracellular (outside cells)

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87
Q

What are enzymes made of?

A

Proteins

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88
Q

What is the active site of an enzyme?

A

The part of the enzyme where substrate molecules bind

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89
Q

Why are enzymes highly specific?

A

Due to their tertiary structure

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90
Q

What is activation energy?

A

The energy required to start a chemical reaction

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91
Q

How do enzymes affect activation energy?

A

They lower the amount of activation energy needed

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92
Q

What is the enzyme-substrate complex?

A

Formed when a substrate fits into the enzyme’s active site

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93
Q

What are the two reasons enzymes lower activation energy?

A
  • Holds substrate molecules close together * Puts strain on bonds in the substrate
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94
Q

What does the ‘lock and key’ model describe?

A

How a substrate fits into an enzyme’s active site

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95
Q

What is the ‘induced fit’ model?

A

The substrate binding changes the shape of the active site slightly

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96
Q

Why is the ‘induced fit’ model considered a better theory?

A

It explains the specificity of enzymes and their binding to substrates

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97
Q

What determines the active site’s shape?

A

The enzyme’s tertiary structure

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98
Q

What happens if the tertiary structure of an enzyme is altered?

A

The active site changes shape and the substrate may not fit

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99
Q

What factors can alter the tertiary structure of an enzyme?

A
  • Changes in pH * Changes in temperature
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100
Q

How does enzyme concentration affect the rate of reaction?

A

More enzyme molecules increase the likelihood of substrate collisions

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101
Q

What limits the effect of increasing enzyme concentration?

A

Limited substrate availability

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102
Q

How does substrate concentration affect the rate of reaction?

A

Higher substrate concentration increases reaction rate up to a saturation point

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103
Q

What happens to substrate concentration over time during a reaction?

A

It decreases unless more substrate is added

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104
Q

What is the initial rate of reaction?

A

The highest rate of reaction at the start due to maximum substrate availability

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105
Q

What is an enzyme?

A

A biological catalyst that speeds up chemical reactions in living organisms.

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106
Q

How can you measure the rate of an enzyme-controlled reaction?

A

By measuring how fast the product of the reaction is made or how fast the substrate is removed.

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107
Q

What does catalase catalyze?

A

The breakdown of hydrogen peroxide into water and oxygen.

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108
Q

What is the role of a buffer solution in enzyme experiments?

A

To resist changes in pH when small amounts of acid or alkali are added.

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109
Q

Fill in the blank: The initial rate of reaction is the rate right at the start of the reaction, close to time equals _______.

A

zero

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110
Q

What is the formula to calculate the gradient of a tangent on a graph?

A

Gradient = change in y axis ÷ change in x axis.

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111
Q

What is the initial rate of reaction if the volume of product released is 50 cm³ over 18 seconds?

A

2.8 cm³ s⁻¹.

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112
Q

True or False: A straight line at the start of the reaction means you need to draw a tangent.

A

False

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113
Q

What is the name given to the amount of energy needed to start a reaction?

A

Activation energy.

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114
Q

What is an enzyme-substrate complex?

A

A temporary complex formed when an enzyme binds to its substrate.

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115
Q

What color change indicates the presence of starch in a solution?

A

It turns a dark blue-black color.

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116
Q

How does amylase affect starch concentration?

A

It catalyzes the breakdown of starch into maltose.

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117
Q

What is the purpose of a negative control in enzyme experiments?

A

To ensure that any observed effect is due to the enzyme and not other factors.

118
Q

Fill in the blank: The absorbance of the solution is measured using a _______.

A

colorimeter

119
Q

What happens to the absorbance reading as starch is broken down by amylase?

A

The absorbance decreases.

120
Q

What should be done to maintain consistent conditions during an enzyme reaction experiment?

A

Keep the volume and concentration of substrate solution the same.

121
Q

How can you calculate the average initial rate of reaction for different enzyme concentrations?

A

By repeating the experiment and averaging the data collected.

122
Q

What does the gradient of a straight line on a graph indicate?

A

The rate of reaction.

123
Q

True or False: The unit of absorbance has its own proper unit of measurement.

A

False

124
Q

What should be included in experiments to compare the effect of different enzyme concentrations?

A

A negative control experiment.

125
Q

What are the two types of nucleic acid?

A

DNA (deoxyribonucleic acid) and RNA (ribonucleic acid)

Both types carry important genetic information in living cells.

126
Q

What is the main function of DNA?

A

To store genetic information necessary for the growth and development of an organism

DNA contains all the instructions from fertilization to adulthood.

127
Q

What is the role of RNA in relation to DNA?

A

To transfer genetic information from DNA to ribosomes

Ribosomes read the RNA to synthesize proteins through translation.

128
Q

Define a mononucleotide.

A

A biological molecule made from a pentose sugar, a nitrogen-containing organic base, and a phosphate group

Mononucleotides are the building blocks of DNA and RNA.

129
Q

What is the sugar found in DNA mononucleotides?

A

Deoxyribose

Each DNA mononucleotide has a phosphate group and one of four bases.

130
Q

What are the four possible bases in DNA?

A
  • Adenine (A)
  • Thymine (T)
  • Cytosine (C)
  • Guanine (G)

The base can vary in each DNA mononucleotide.

131
Q

What sugar is found in RNA mononucleotides?

A

Ribose

RNA mononucleotides also contain a phosphate group and one of four bases.

132
Q

What base replaces thymine in RNA?

A

Uracil (U)

RNA contains adenine, uracil, cytosine, and guanine as its bases.

133
Q

What is a polynucleotide?

A

A polymer of mononucleotides

Both DNA and RNA are formed from polynucleotides.

134
Q

How are mononucleotides joined together?

A

Through condensation reactions between the phosphate of one mononucleotide and the sugar of another

Water is a by-product of this reaction.

135
Q

How many strands does DNA have?

A

Two polynucleotide strands

RNA has just one strand.

136
Q

What kind of structure does DNA have?

A

A double-helix structure

This structure helps DNA to carry out its function.

137
Q

What is complementary base pairing?

A

The specific pairing of bases in DNA: adenine pairs with thymine (A - T), and cytosine pairs with guanine (C - G)

This ensures equal amounts of A & T and C & G in DNA.

138
Q

How many hydrogen bonds form between adenine and thymine?

A

Two hydrogen bonds

Three hydrogen bonds form between cytosine and guanine.

139
Q

True or False: DNA was first observed in the 1800s.

A

True

Initial doubts existed regarding DNA’s ability to carry genetic information due to its simple chemical composition.

140
Q

By what year was it established that DNA carries the genetic code?

A

1953

This year also marked the determination of the double-helix structure.

141
Q

Fill in the blank: RNA is made up of a single polynucleotide strand, whereas DNA is made up of _______.

A

two strands

DNA strands are joined by hydrogen bonds.

142
Q

What is a gene?

A

A sequence of mononucleotide bases on a DNA molecule that codes for the sequence of amino acids in a polypeptide.

143
Q

How does the sequence of bases in a gene affect protein synthesis?

A

The order of mononucleotide bases determines the order of amino acids in a particular protein.

144
Q

What is a triplet in the context of genetics?

A

A sequence of three bases in a gene that codes for a specific amino acid.

145
Q

What process involves copying DNA into mRNA?

A

Transcription.

146
Q

What is the function of mRNA?

A

Carries the genetic code from the DNA in the nucleus to the cytoplasm for protein synthesis.

147
Q

What is the role of ribosomes in protein synthesis?

A

Ribosomes are the organelles that synthesize proteins using mRNA.

148
Q

What is the structure of RNA compared to DNA?

A

RNA is a single polynucleotide strand and contains uracil (U) instead of thymine.

149
Q

What is the function of transfer RNA (tRNA)?

A

Carries amino acids to the ribosomes during translation.

150
Q

What are codons?

A

Three adjacent bases in mRNA that correspond to specific amino acids.

151
Q

What are anticodons?

A

A sequence of three bases on tRNA that pairs with the codons on mRNA.

152
Q

True or False: The genetic code is overlapping.

A

False.

153
Q

What does it mean that the genetic code is degenerate?

A

There are more possible combinations of triplets (64) than there are amino acids (20), meaning some amino acids are coded by multiple triplets.

154
Q

What are start and stop codons?

A

Codons that signal the beginning and end of protein synthesis.

155
Q

Fill in the blank: The process of synthesizing proteins from mRNA is called _______.

A

Translation.

156
Q

What is the significance of the sequence GUG in mRNA?

A

It codes for a specific amino acid (Valine).

157
Q

What type of bonds form between codons and anticodons during protein synthesis?

A

Hydrogen bonds.

158
Q

What is the primary purpose of mRNA in the cell?

A

To serve as a template for protein synthesis.

159
Q

What is the first stage of protein synthesis called?

A

Transcription

160
Q

Where does transcription occur?

A

In the nucleus

161
Q

What enzyme initiates transcription?

A

RNA polymerase

162
Q

What happens to the DNA double-helix during transcription?

A

The hydrogen bonds break and the strands separate

163
Q

What is the DNA template strand also known as?

A

Antisense strand

164
Q

What replaces thymine (T) in RNA during transcription?

A

Uracil (U)

165
Q

What is formed from the RNA mononucleotides during transcription?

A

An mRNA molecule

166
Q

What happens when RNA polymerase reaches a stop codon?

A

It stops making mRNA and detaches from the DNA

167
Q

What is the second stage of protein synthesis called?

A

Translation

168
Q

Where does translation take place?

A

In the cytoplasm

169
Q

What do tRNA molecules carry to the ribosome during translation?

A

Amino acids

170
Q

How does a tRNA molecule attach to the mRNA?

A

By complementary base pairing

171
Q

What type of bond is formed between amino acids during translation?

A

Peptide bond

172
Q

What is the end product of protein synthesis?

A

A polypeptide chain

173
Q

What happens to the polypeptide chain after translation is complete?

A

It moves away from the ribosome

174
Q

Fill in the blank: The process of protein synthesis is also called _______.

A

Polypeptide synthesis

175
Q

True or False: The ribosome moves along the mRNA during translation.

A

True

176
Q

What must occur for translation to continue until completion?

A

A stop codon must be reached

177
Q

What sequence is GCGAAGTCCATG complementary to in mRNA?

A

CGCUUCA GG UAC

178
Q

What is the sequence of tRNA anticodons for the mRNA sequence CGCUUCA GG UAC?

A

CGA AGU CUG AUG

179
Q

How long would the mRNA be in mononucleotides for a polypeptide chain of 10 amino acids?

A

30 nucleotides long

180
Q

What does a drug that prevents RNA polymerase from binding to DNA affect?

A

Protein synthesis

181
Q

What is the process by which DNA replicates itself before cell division?

A

Semi-conservative replication

Each new DNA molecule contains one strand from the original DNA molecule and one new strand.

182
Q

What enzyme breaks the hydrogen bonds between bases during DNA replication?

A

DNA helicase

This unwinding creates two single strands of DNA.

183
Q

What is the role of complementary base pairing in DNA replication?

A

Free-floating DNA nucleotides are attracted to their complementary exposed bases on each original template strand: A with T and C with G.

184
Q

What enzyme catalyzes the condensation reactions that join nucleotides of the new DNA strands together?

A

DNA polymerase

This enzyme also facilitates the formation of hydrogen bonds between the bases on the original and new strands.

185
Q

True or False: In semi-conservative replication, the original DNA strands remain together.

A

False

In semi-conservative replication, each new DNA molecule contains one old and one new strand.

186
Q

What two isotopes of nitrogen were used in Meselson and Stahl’s experiment?

A

Heavy nitrogen (15N) and light nitrogen (14N)

These isotopes helped demonstrate the semi-conservative method of DNA replication.

187
Q

What was the outcome of Meselson and Stahl’s experiment regarding the position of DNA in the centrifuge?

A

DNA settled out in the middle

This indicated that the DNA molecules contained a mixture of heavy and light nitrogen.

188
Q

Fill in the blank: Each original single strand of DNA acts as a _______ for a new strand.

A

template

189
Q

What is the key difference between conservative and semi-conservative theories of DNA replication?

A

In conservative replication, original strands stay together; in semi-conservative, each new DNA molecule has one original and one new strand.

190
Q

How does hydrogen bonding occur during DNA replication?

A

Hydrogen bonds form between bases on the original and new strands.

191
Q

What happens to bacteria grown in heavy nitrogen broth when transferred to light nitrogen broth?

A

They replicate DNA using both heavy and light nitrogen, resulting in DNA that settles in the middle of the centrifuge.

192
Q

Describe the first step in the semi-conservative replication of DNA.

A

DNA helicase breaks the hydrogen bonds, unwinding the double helix into two single strands.

193
Q

What does the term ‘semi-conservative replication’ mean?

A

It refers to the process where each new DNA molecule consists of one old strand and one newly synthesized strand.

194
Q

Explain the significance of the Meselson and Stahl experiment.

A

It provided evidence that DNA replication is semi-conservative by showing that DNA contains both heavy and light nitrogen after replication.

195
Q

What is the process by which DNA replicates itself before cell division?

A

Semi-conservative replication

Each new DNA molecule consists of one original strand and one newly synthesized strand.

196
Q

What is the role of the enzyme DNA helicase in DNA replication?

A

Breaks the hydrogen bonds between bases on the two polynucleotide DNA strands

This unwinds the DNA helix to form two single strands.

197
Q

What is complementary base pairing in DNA replication?

A

Free-floating DNA nucleotides are attracted to their complementary exposed bases

A pairs with T, and C pairs with G.

198
Q

What enzyme catalyzes the joining of nucleotides in new DNA strands?

A

DNA polymerase

This enzyme is responsible for forming the new DNA strands during replication.

199
Q

Who conducted the experiment that provided evidence for semi-conservative replication?

A

Meselson and Stahl

Their experiment used isotopes of nitrogen to demonstrate the mechanism of DNA replication.

200
Q

What isotopes of nitrogen were used in Meselson and Stahl’s experiment?

A

Heavy nitrogen (15N) and light nitrogen (14N)

These isotopes helped differentiate between old and new DNA strands.

201
Q

What would happen if DNA replication was conservative according to Meselson and Stahl’s experiment?

A

The original heavy DNA would stay together, and new light DNA would settle at the top

This would result in distinct layers in the centrifuge.

202
Q

What was the outcome of Meselson and Stahl’s experiment after one round of replication in light nitrogen?

A

The DNA settled out in the middle, indicating a mixture of heavy and light nitrogen

This supported the theory of semi-conservative replication.

203
Q

Fill in the blank: Each new DNA molecule contains one strand from the _______ DNA molecule and one new strand.

A

[original]

This illustrates the semi-conservative nature of DNA replication.

204
Q

True or False: In semi-conservative replication, both strands of the new DNA molecule are completely new.

A

False

One strand is from the original DNA and one strand is newly synthesized.

205
Q

What happens during condensation reactions in DNA replication?

A

Nucleotides of the new strands are joined together

This process is essential for forming the backbone of the new DNA strands.

206
Q

What is the significance of hydrogen bonds in DNA replication?

A

They form between the bases on the original and new strands

This stabilizes the new DNA structure.

207
Q

What happens to the DNA after it is spun in a centrifuge during Meselson and Stahl’s experiment?

A

The DNA settles at different levels based on its density

Heavy DNA settles lower than light DNA.

208
Q

Describe the key difference between conservative and semi-conservative DNA replication.

A

In conservative replication, the original strands stay together; in semi-conservative, each new DNA contains one original and one new strand

This distinction is critical in understanding DNA replication mechanisms.

209
Q

What is the process by which DNA replicates itself before cell division?

A

Semi-conservative replication

Each new DNA molecule consists of one original strand and one newly synthesized strand.

210
Q

What is the role of the enzyme DNA helicase in DNA replication?

A

Breaks the hydrogen bonds between bases on the two polynucleotide DNA strands

This unwinds the DNA helix to form two single strands.

211
Q

What is complementary base pairing in DNA replication?

A

Free-floating DNA nucleotides are attracted to their complementary exposed bases

A pairs with T, and C pairs with G.

212
Q

What enzyme catalyzes the joining of nucleotides in new DNA strands?

A

DNA polymerase

This enzyme is responsible for forming the new DNA strands during replication.

213
Q

Who conducted the experiment that provided evidence for semi-conservative replication?

A

Meselson and Stahl

Their experiment used isotopes of nitrogen to demonstrate the mechanism of DNA replication.

214
Q

What isotopes of nitrogen were used in Meselson and Stahl’s experiment?

A

Heavy nitrogen (15N) and light nitrogen (14N)

These isotopes helped differentiate between old and new DNA strands.

215
Q

What would happen if DNA replication was conservative according to Meselson and Stahl’s experiment?

A

The original heavy DNA would stay together, and new light DNA would settle at the top

This would result in distinct layers in the centrifuge.

216
Q

What was the outcome of Meselson and Stahl’s experiment after one round of replication in light nitrogen?

A

The DNA settled out in the middle, indicating a mixture of heavy and light nitrogen

This supported the theory of semi-conservative replication.

217
Q

Fill in the blank: Each new DNA molecule contains one strand from the _______ DNA molecule and one new strand.

A

[original]

This illustrates the semi-conservative nature of DNA replication.

218
Q

True or False: In semi-conservative replication, both strands of the new DNA molecule are completely new.

A

False

One strand is from the original DNA and one strand is newly synthesized.

219
Q

What happens during condensation reactions in DNA replication?

A

Nucleotides of the new strands are joined together

This process is essential for forming the backbone of the new DNA strands.

220
Q

What is the significance of hydrogen bonds in DNA replication?

A

They form between the bases on the original and new strands

This stabilizes the new DNA structure.

221
Q

What happens to the DNA after it is spun in a centrifuge during Meselson and Stahl’s experiment?

A

The DNA settles at different levels based on its density

Heavy DNA settles lower than light DNA.

222
Q

Describe the key difference between conservative and semi-conservative DNA replication.

A

In conservative replication, the original strands stay together; in semi-conservative, each new DNA contains one original and one new strand

This distinction is critical in understanding DNA replication mechanisms.

223
Q

What are mutations?

A

Changes to the base sequence of DNA caused by errors during DNA replication.

Types of errors include deletion, insertion, and substitution.

224
Q

What is deletion in the context of mutations?

A

One base is deleted from the DNA sequence, e.g., ATGCT becomes ATCCT.

This can affect the resulting protein.

225
Q

What is insertion in the context of mutations?

A

An extra base is added to the DNA sequence, e.g., ATGCT becomes ATGACT.

This can alter the amino acid sequence in proteins.

226
Q

What is inversion in the context of mutations?

A

A sequence of bases is reversed, e.g., ATCT becomes ATTC.

This can impact protein function.

227
Q

How can mutations affect proteins?

A

Mutations can change the final 3D shape of the protein, potentially leading to dysfunction.

Example: Cystic fibrosis results from mutations affecting mucus production.

228
Q

What is cystic fibrosis?

A

A genetic disorder caused by mutations in a gene important for mucus production.

Over 1000 mutations are known to cause CF.

229
Q

What is monohybrid inheritance?

A

The inheritance of a single characteristic controlled by different alleles.

Genetic diagrams can predict the genotypes and phenotypes of offspring.

230
Q

What is the dominant allele for plant height in pea plants?

A

The allele for tall plants (T) is dominant over the allele for dwarf plants (t).

231
Q

What is the predicted genotype ratio when two heterozygous pea plants (Tt) are crossed?

A

1 TT : 2 Tt : 1 tt

This results in a phenotypic ratio of 3 tall : 1 dwarf.

232
Q

Define ‘gene’.

A

A sequence of bases on a DNA molecule that codes for a protein, resulting in a characteristic.

233
Q

Define ‘allele’.

A

A different version of a gene that can have slightly different base sequences, e.g., brown eyes (B) and blue eyes (b).

234
Q

What is a genotype?

A

The alleles a person has, e.g., BB, Bb, or bb for a trait.

235
Q

What is a phenotype?

A

The characteristics displayed by an organism, e.g., brown eyes.

236
Q

What is a dominant allele?

A

An allele whose characteristic appears in the phenotype even when only one copy is present.

237
Q

What is a recessive allele?

A

An allele whose characteristic only appears in the phenotype if two copies are present.

238
Q

What is incomplete dominance?

A

When the trait from a dominant allele isn’t completely shown over the trait produced by the recessive allele.

239
Q

Define ‘homozygote’.

A

An organism that carries two copies of the same allele for a certain characteristic.

240
Q

Define ‘heterozygote’.

A

An organism that carries two different alleles for a certain characteristic.

241
Q

True or False: The allele for yellow seeds in garden pea plants is recessive.

A

False

The allele for yellow seeds (Y) is dominant over the allele for green seeds (y).

242
Q

What is the predicted ratio of green seeds to yellow seeds in the offspring when a heterozygous plant is crossed with a homozygous plant with green seeds?

A

1 green : 1 yellow

This is based on the genotype of the parents.

243
Q

What is the purpose of the Chi-Squared Test?

A

To check the results of genetic crosses and determine if observed results support a theory.

244
Q

What is the expected result in a Chi-Squared Test?

A

The predicted result based on a hypothesis.

245
Q

What is the observed result in a Chi-Squared Test?

A

The actual result recorded from the experiment.

246
Q

What is the null hypothesis?

A

There is no significant difference between observed and expected results.

247
Q

What does it mean if the Chi-Squared Test shows no significant difference?

A

The null hypothesis cannot be rejected, supporting the theory.

248
Q

What is the formula for calculating Chi-Squared (χ²)?

A

χ² = Σ((O - E)² / E) where O = observed result and E = expected result.

249
Q

What is the expected phenotypic ratio for normal and vestigial wings in fruit flies according to monohybrid inheritance?

A

3:1 ratio of normal : vestigial wings.

250
Q

How do you calculate the expected number of offspring with normal wings if 160 offspring are produced?

A

160 ÷ 4 × 3 = 120.

251
Q

How do you calculate the expected number of offspring with vestigial wings if 160 offspring are produced?

A

160 ÷ 4 × 1 = 40.

252
Q

If the calculated Chi-Squared value is 2.7 and the critical value is 3.84, what can be concluded?

A

There is no significant difference; fail to reject the null hypothesis.

253
Q

What is the probability level commonly used in biological studies for the Chi-Squared Test?

A

0.05 (5%).

254
Q

How do you determine the degrees of freedom for a Chi-Squared Test?

A

Number of classes (phenotypes) minus one.

255
Q

What is the critical value at one degree of freedom for a probability level of 0.05?

A

3.84.

256
Q

True or False: The Chi-Squared Test can prove that a hypothesis is true.

A

False.

257
Q

Fill in the blank: The Chi-Squared Test is used to test theories about the _______ of characteristics.

A

[inheritance]

258
Q

What does it mean to ‘fail to reject’ the null hypothesis?

A

The evidence does not provide a reason to think the hypothesis is wrong.

259
Q

What are the steps to perform a Chi-Squared Test?

A
  1. State the null hypothesis. 2. Calculate expected results. 3. Collect observed results. 4. Calculate χ² value. 5. Compare χ² value to critical value.
260
Q

In the context of the Chi-Squared Test, what does ‘O - E’ represent?

A

The difference between the observed and expected results.

261
Q

What is cystic fibrosis (CF)?

A

An inherited disorder that mainly affects the respiratory, digestive, and reproductive systems

CF is caused by a recessive allele, meaning an individual must inherit one recessive allele from each parent to have the disorder.

262
Q

How do individuals inherit cystic fibrosis?

A

Individuals must be homozygous for the CF allele (ff) to have the disorder

Heterozygous individuals (Ff) are carriers but do not have the disorder.

263
Q

What does a genetic pedigree diagram illustrate?

A

It shows how traits, such as cystic fibrosis, run in families

The diagram uses symbols to represent affected and unaffected individuals.

264
Q

What is the chance that two carrier parents will have a child with cystic fibrosis?

A

25% chance

This is calculated using a genetic diagram.

265
Q

What is CFTR?

A

Cystic Fibrosis Transmembrane Conductance Regulator, a channel protein that transports chloride ions out of cells

A mutation in the gene coding for CFTR causes cystic fibrosis.

266
Q

What is the effect of the CFTR mutation on mucus production?

A

It results in thick, sticky mucus due to less chloride ions moving out of cells

This causes problems in the respiratory, digestive, and reproductive systems.

267
Q

How does cystic fibrosis affect the respiratory system?

A

Thick mucus builds up in airways, reducing gas exchange and increasing the risk of lung infections

Cilia cannot move the thick mucus towards the throat.

268
Q

What digestive issues are caused by cystic fibrosis?

A

Blocked pancreatic ducts prevent digestive enzymes from reaching the small intestine, leading to poor nutrient absorption

Thick mucus can also cause cysts in the pancreas.

269
Q

How does cystic fibrosis impact the reproductive system in males?

A

Tubes connecting the testicles to the penis can be absent or blocked, preventing sperm from reaching the penis

This results in infertility for some men with CF.

270
Q

How does cystic fibrosis affect female reproduction?

A

Thick cervical mucus can prevent sperm from reaching the egg, reducing sperm motility

This can lead to difficulties in conception for women with CF.

271
Q

Fill in the blank: Individuals with cystic fibrosis inherit _______ alleles from both parents.

A

recessive

272
Q

True or False: Carriers of cystic fibrosis have the disorder.

A

False

Carriers have one normal and one cystic fibrosis allele (Ff) but do not exhibit symptoms.

273
Q

What role does mucus play in the respiratory system?

A

It helps prevent lung infections by trapping microorganisms

Mucus is normally moved towards the throat by cilia.

274
Q

What is the significance of the key in a genetic pedigree diagram?

A

It explains what the shapes represent, indicating affected and unaffected individuals

This helps in understanding the inheritance pattern of traits.

275
Q

What are the three main uses of genetic screening?

A
  • Identification of Carriers
  • Preimplantation Genetic Diagnosis (PGD)
  • Prenatal Testing

Each use has specific implications and ethical considerations.

276
Q

What is carrier testing?

A

Carrier testing is offered to individuals with a family history of genetic disorders.

It identifies individuals who carry a gene for a specific genetic disorder.

277
Q

What are some ethical issues raised by carrier testing?

A
  • Tests aren’t always 100% accurate
  • Other genetic abnormalities may be found
  • Concerns about genetic discrimination

These issues can lead to stress and potential misuse of information.

278
Q

What is Preimplantation Genetic Diagnosis (PGD)?

A

PGD is carried out on embryos produced by in vitro fertilization (IVF) to screen for genetic disorders before implantation.

This process helps reduce the chance of having a baby with genetic disorders.

279
Q

What are the advantages of PGD?

A
  • Reduces the chance of genetic disorders
  • Avoids the issue of abortion related to prenatal testing

Only embryos without the tested genetic disorders will be implanted.

280
Q

What ethical issues are associated with PGD?

A
  • Can be used to select for characteristics like gender
  • False results could provide incorrect information

This raises concerns about ‘designer babies’ and the potential for misuse.

281
Q

What is prenatal testing?

A

Prenatal tests involve screening unborn babies for genetic disorders offered to pregnant women with a family history of genetic disease.

It includes procedures like amniocentesis and chorionic villus sampling.

282
Q

What is amniocentesis?

A
  • Usually carried out at 15-20 weeks of pregnancy
  • Involves obtaining a sample of amniotic fluid
  • Has a 1% risk of miscarriage

Results take 2-3 weeks, with rapid tests available in 3-4 days.

283
Q

What is chorionic villus sampling (CVS)?

A
  • Performed at 11-14 weeks of pregnancy
  • Involves taking a sample from chorionic villi
  • Has a 1-2% risk of miscarriage

Initial results are available in a few days, but detailed results take longer.

284
Q

What are the benefits of prenatal testing?

A
  • Allows informed decisions for parents
  • Helps prepare for future care of the child

Positive test results can lead to decisions about childbirth or abortion.

285
Q

What are some ethical issues associated with prenatal testing?

A
  • Slightly increases the risk of miscarriage
  • False results could provide incorrect information
  • Ethical concerns about aborting a fetus with a genetic disorder

These issues can lead to moral dilemmas for parents.

286
Q

True or False: Chorionic villus sampling (CVS) has a lower risk of miscarriage than amniocentesis.

A

False

CVS has a higher risk of miscarriage compared to amniocentesis.

287
Q

Fill in the blank: Duchenne muscular dystrophy is a genetic disorder caused by a _______.

A

recessive allele

It is caused by a mutated gene that codes for a protein needed for healthy muscle tissue.

288
Q

What is one reason why individuals with a family history of Duchenne muscular dystrophy may be offered carrier testing?

A

To determine if they carry a gene for Duchenne muscular dystrophy.

This helps assess the risk of passing the disorder to offspring.

289
Q

Describe one benefit of preimplantation genetic diagnosis (PGD).

A

It reduces the chance of having a baby with a genetic disorder.

Only healthy embryos are selected for implantation.

290
Q

List two social or ethical issues raised by preimplantation genetic diagnosis.

A
  • Potential for ‘designer babies’
  • False results providing incorrect information

These issues raise concerns about the future of genetic selection.

Biology Edexcel Sophie (8 decks)

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