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OCR Biology A for AS and A-Level > Module 2 > Flashcards

Module 2 Flashcards

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1
Q

What is the main difference between gram positive and gram negative bacteria?

A

Gram positive bacteria have thicker cell walls which can hold the gram-stain. Gram negative bacteria are counter-stained red

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2
Q

How is image magnification calculated?

A

Magnification equals ‘size of image’ divided by ‘actual size’

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3
Q

What are the main differences between light microscopes and electron microscopes?

A

Electron microscopes require a vacuum to operate, produce a black and white image, and can magnify up to 500000 times, but specimens must be dead. Light microscopes can only magnify up to 2000 times, but specimens can be alive

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4
Q

Describe the features of a Eukaryotic nucleus, including the nucleolus

A

The nucleus contains the cell’s DNA, wrapped in histone-complexes during interphase, to form chromatin. It has a double membrane and within it lies the nucleolus, which is the site of ribosome production

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5
Q

Outline the structure and basic role of mitochondria

A

Mitochondria are the site of the final stages of cellular respiration, and have two membranes. The inner membrane contains folds called cristae and holds the matrix (fluid). Mitochondria also have their own DNA, known as mtDNA

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6
Q

What are Vesicles and lysosomes?

A

Vesicles are membranous sacs which transport molecules in a cell. Lysosomes are vesicles with hydrolytic enzymes, which break down waste products

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7
Q

What is the Cytoskeleton (of a eukaryotic cell)?

A

The cytoskeleton is a three-component system that gives support. Microfilaments control movement, microtubules provide structure and intermediate-fibres give the cell strength and rigidity

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8
Q

What are centrioles?

A

Centrioles are an extra component of the cytoskeleton composed of microtubules - a pair is called a centrosome - they organise the spindle fibres in mitosis

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9
Q

What are the smooth and rough endoplasmic reticula?

A

The smooth endoplasmic reticulum synthesises lipids and carbohydrates and the rough endoplasmic reticulum (which can be identified by the ribosomes on its surface) synthesises proteins from amino acids

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10
Q

What is the role of the Golgi apparatus?

A

The modify and package proteins (into vesicles)

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11
Q

What is the cell wall made from in a plant cell?

A

Cellulose

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12
Q

What is a vacuole and what is the name given to its membrane?

A

A vacuole is a sac of sap in the cytoplasm of plant cells that helps to maintain turgor, its membrane is called a tonoplast

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13
Q

What is the basic structure and function of a chloroplast?

A

Chloroplasts are the organelle involved in photosynthesis. They have a double membrane which contains a stroma (fluid) and thylakoids, which are connected by lamellae. A stack of thylakoids is called a granum. Starch grains can also often be found in the stroma

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14
Q

List three main differences between the structure of prokaryotic and eukaryotic cells

A

Prokaryotic cells contain a small molecule of DNA, with many operons, and have 70-subunit (70s) ribosomes, instead of 80s, and have no membrane bound organelles

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15
Q

Briefly explain the theory of endosymbiosis

A

The suggestion that mitochondria and chloroplasts were once free-living prokaryotes who migrated into other cells

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16
Q

What is the difference between alpha and beta glucose?

A

Alpha glucose has the OH group ‘that switches places’ at the ‘bottom’ of the molecule / below the plane

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17
Q

Which polysaccharides does alpha glucose form?

A

1-4 Amylose and 1-4/1-6 Amylopectin A.K.A: Starch and also glycogen (branched). Both are insoluble

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18
Q

Which polysaccharides does beta glucose alternate to form?

A

Cellulose, which is straight and unbranched

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19
Q

Explain Benedict’s Test for Reducing Sugars

A

Reducing Sugars reduce copper (2+) ions of the solution and turn it progressively ‘redder’ after boiling

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20
Q

Explain Benedict’s Test for Non-Reducing Sugars

A

The sugars are boiled with hydrochloric acid and sodium hydrogen carbonate is added to neutralise the solution. Then the reagent is added and boiled again - the non-reducing sugars now show a colour change

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21
Q

Explain the Iodine Test

A

A test for starch, where aqueous iodine is added and a positive result turns the solution (from orange) to purple/black

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22
Q

How are triglycerides formed?

A

A molecule of glycerol binds to 3 fatty acid chains in a condensation reaction (making ester bonds)

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23
Q

Which type of fats are considered more healthy?

A

Unsaturated fats

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24
Q

What are sterols?

A

sterols are complex alcohol molecules (such as cholesterol)

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25
Q

Explain the Emulsion Test

A

This tests for lipids and fats. When the sample is mixed with ethanol and water, a cloudy white emulsion will form if lipids are present

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26
Q

What is a peptide bond and how is it formed?

A

A peptide bond is a bond between a carboxylic acid group and an amine group, formed by condensation

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27
Q

Explain the four levels of protein structure

A

Primary: sequence of amino acids
Secondary: hydrogen bonding into alpha-helices and beta-pleated sheets
Tertiary: Final folding, inter-molecular forces and disulphide bridges, hydrophobic r-groups fold inwards, away from water
Quarternary: Combination of multiple protein subunits to make enzymes and hormones

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28
Q

Explain the Biuret Test

A

It identifies proteins, the biuret solution (NaOH and copper sulphate) turns lilac/violet if positive

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29
Q

What are the three main protein types?

A

Globular: compact and generally water soluble
Fibrous: long and insoluble
Conjugate: contain a non-protein prosthetic group

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30
Q

Describe Keratin

A

A strong, protein in hair and nails

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31
Q

Describe Elastin

A

A fibrous protein in blood vessels, made from flexible ‘tropoelastin’

32
Q

Describe Collagen

A

A connective protein in skin and tendons, made of a triple helix of tropocollagen

33
Q

What are the bonds what link nucleic acids in DNA?

A

Phosphodiester bonds

34
Q

Which nitrogenous bases form 3 hydrogen bonds between one another?

A

C-G (Cytosine to Guanine)

35
Q

Which nitrogenous bases form 2 hydrogen bonds between one another?

A

T-A (Thymine to Adenine)

36
Q

Which nitrogenous bases are Purines (two-ringed)?

A

Adenine and Guanine

37
Q

Which nitrogenous bases are Pyrimidines (one-ringed)?

A

Thymine and Cytosine

38
Q

Which two principles dictate DNA structure?

A

Complementary Base Pairing

Antiparallel backbones

39
Q

How can DNA be extracted?

A

Use a detergent to break the membrane, add a salt, protease and alcohol, the DNA will precipitate out

40
Q

Name the process and enzymes involved in Semiconservative Replication

A

DNA Helicase ‘unzips’ the double helix
Free floating nucleotides are joined on by DNA-polymerase (condensation reaction) and two new strands are formed - each with half of the initial bases

41
Q

Which direction does DNA-polymerase travel in?

A

3’ to 5’, continuously up the leading strand

42
Q

How does DNA-polymerase replicate the lagging strand?

A

It replicates backwards in stages called Okazaki Fragments, from the lagging strands 3’ end to its 5’ end

43
Q

Why is DNA known as a degenerate code?

A

Multiple codons code for the same amino acids and there are also dedicated start and stop codons

44
Q

Explain the process of Transcription

A

RNA-polymerase uses the antisense strand (3’ to 5’) as a template to produce mRNA

45
Q

Explain the process of Translation

A

mRNA binds to ribosome subunits where tRNA pairs complementary anticodons to produce the primary structure of amino acids. Helped by peptidyl transferase

46
Q

What are Saprophytes?

A

Organisms such as fungi that have extracellular digestive enzymes

47
Q

Name two enzymes that digest starch and state where they are found

A

Amylase in salivary glands and maltase in the small intestine

48
Q

What enzyme digests large proteins and where is it released?

A

Trypsin, from the pancreas

49
Q

What is a Q-10 value?

A

A measure of the increase in rate of an enzymes metabolism after a 10-degree increase in temperature

50
Q

When do enzymes denature?

A

When they far exceed their optimum temperature or encounter pH extremes

51
Q

Name the three types of enzyme inhibition

A

Competitive (temporary)
Non-Competitive (often permanent)
End-product Inhibition (part of negative feedback mechanisms)

52
Q

What is compartmentalisation?

A

Formation of membranes between organelles to maintain chemical gradients

53
Q

What is the plasma membrane?

A

The membrane that separates the cell from its ‘outside’

54
Q

What are the principles of the Fluid Mosaic Model?

A

That the phospholipids in the bilayer are free to move relative to each other, and that their fluidity is controlled by cholesterol, which also stops crystallisation

55
Q

What are channel proteins?

A

Intrinsic passive passages for ions etc.

56
Q

What are carrier proteins?

A

Intrinsic active passages

57
Q

What is the role of Glycoprotein?

A

Adhesion and cell signalling

58
Q

What is the role of Glycolipids?

A

Act as cell markers (antigens)

59
Q

How does an increase in temperature change the plasma membrane?

A

Increases fluidity, will eventually cause denaturing

60
Q

How can solvents change the plasma membrane?

A

less-polar organic solvents, such as alcohols, can disrupt and dissolve the membranes

61
Q

What is facilitated diffusion?

A

The passive movement of molecules or ions through carrier proteins, considered selectively permeable

62
Q

What is bulk transport?

A

The vesicular, active transport of solids (phagocytosis) and liquids (pinocytosis) both in and our of cells

63
Q

What happens in G1 and G2 of the cell cycle?

A

Cell grows in size and organelles are duplicated

64
Q

What happens during S phase of the cell cycle?

A

DNA copied and chromosomes are replicated

65
Q

Why do cells enter G0 of the cell cycle?

A

To either differentiate or senesce

66
Q

What is checked at the G1 and G2 checkpoints?

A

Size and growth, and DNA quality after replication

67
Q

What happens to the number of chromatids during replication?

A

It doubles

68
Q

Explain the Stages of Mitosis

A

Prophase: Chromatin condenses and centrioles begin to attach spindle fibres centromeres
Metaphase: Chromosomes line up to form metaphase plate
Anaphase: Centromeres divide, chromosomes pull apart
Telophase: Chromosomes reassemble, nucleus reforms

69
Q

Summarise the key features of Meiosis 1

A

Pairs of homologous chromosomes are separated, known as a reduction phase

70
Q

Summarise the key features of Meiosis 2

A

separates pairs of chromatids

71
Q

What are bivalents?

A

Pairs of homologous chromosomes

72
Q

What key process occurs in Metaphase 1 and 2?

A

chrom(osomes/atids) randomly orientate, causing independent assortment

73
Q

What happens during Anaphase 1?

A

chromatids breaks and rejoin at chiasmata to make recombinant chromatids

74
Q

What are pluripotent stem cells?

A

Those that can form any tissue type but not whole organisms

75
Q

How can you obtain plant stem cells?

A

From meristem and vascular cambium

OCR Biology A for AS and A-Level (5 decks)

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