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

Module 2 Flashcards

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
Explain the Emulsion Test
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
26
What is a peptide bond and how is it formed?
A peptide bond is a bond between a carboxylic acid group and an amine group, formed by condensation
27
Explain the four levels of protein structure
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
28
Explain the Biuret Test
It identifies proteins, the biuret solution (NaOH and copper sulphate) turns lilac/violet if positive
29
What are the three main protein types?
Globular: compact and generally water soluble Fibrous: long and insoluble Conjugate: contain a non-protein prosthetic group
30
Describe Keratin
A strong, protein in hair and nails
31
Describe Elastin
A fibrous protein in blood vessels, made from flexible 'tropoelastin'
32
Describe Collagen
A connective protein in skin and tendons, made of a triple helix of tropocollagen
33
What are the bonds what link nucleic acids in DNA?
Phosphodiester bonds
34
Which nitrogenous bases form 3 hydrogen bonds between one another?
C-G (Cytosine to Guanine)
35
Which nitrogenous bases form 2 hydrogen bonds between one another?
T-A (Thymine to Adenine)
36
Which nitrogenous bases are Purines (two-ringed)?
Adenine and Guanine
37
Which nitrogenous bases are Pyrimidines (one-ringed)?
Thymine and Cytosine
38
Which two principles dictate DNA structure?
Complementary Base Pairing | Antiparallel backbones
39
How can DNA be extracted?
Use a detergent to break the membrane, add a salt, protease and alcohol, the DNA will precipitate out
40
Name the process and enzymes involved in Semiconservative Replication
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
Which direction does DNA-polymerase travel in?
3' to 5', continuously up the leading strand
42
How does DNA-polymerase replicate the lagging strand?
It replicates backwards in stages called Okazaki Fragments, from the lagging strands 3' end to its 5' end
43
Why is DNA known as a degenerate code?
Multiple codons code for the same amino acids and there are also dedicated start and stop codons
44
Explain the process of Transcription
RNA-polymerase uses the antisense strand (3' to 5') as a template to produce mRNA
45
Explain the process of Translation
mRNA binds to ribosome subunits where tRNA pairs complementary anticodons to produce the primary structure of amino acids. Helped by peptidyl transferase
46
What are Saprophytes?
Organisms such as fungi that have extracellular digestive enzymes
47
Name two enzymes that digest starch and state where they are found
Amylase in salivary glands and maltase in the small intestine
48
What enzyme digests large proteins and where is it released?
Trypsin, from the pancreas
49
What is a Q-10 value?
A measure of the increase in rate of an enzymes metabolism after a 10-degree increase in temperature
50
When do enzymes denature?
When they far exceed their optimum temperature or encounter pH extremes
51
Name the three types of enzyme inhibition
Competitive (temporary) Non-Competitive (often permanent) End-product Inhibition (part of negative feedback mechanisms)
52
What is compartmentalisation?
Formation of membranes between organelles to maintain chemical gradients
53
What is the plasma membrane?
The membrane that separates the cell from its 'outside'
54
What are the principles of the Fluid Mosaic Model?
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
What are channel proteins?
Intrinsic passive passages for ions etc.
56
What are carrier proteins?
Intrinsic active passages
57
What is the role of Glycoprotein?
Adhesion and cell signalling
58
What is the role of Glycolipids?
Act as cell markers (antigens)
59
How does an increase in temperature change the plasma membrane?
Increases fluidity, will eventually cause denaturing
60
How can solvents change the plasma membrane?
less-polar organic solvents, such as alcohols, can disrupt and dissolve the membranes
61
What is facilitated diffusion?
The passive movement of molecules or ions through carrier proteins, considered selectively permeable
62
What is bulk transport?
The vesicular, active transport of solids (phagocytosis) and liquids (pinocytosis) both in and our of cells
63
What happens in G1 and G2 of the cell cycle?
Cell grows in size and organelles are duplicated
64
What happens during S phase of the cell cycle?
DNA copied and chromosomes are replicated
65
Why do cells enter G0 of the cell cycle?
To either differentiate or senesce
66
What is checked at the G1 and G2 checkpoints?
Size and growth, and DNA quality after replication
67
What happens to the number of chromatids during replication?
It doubles
68
Explain the Stages of Mitosis
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
Summarise the key features of Meiosis 1
Pairs of homologous chromosomes are separated, known as a reduction phase
70
Summarise the key features of Meiosis 2
separates pairs of chromatids
71
What are bivalents?
Pairs of homologous chromosomes
72
What key process occurs in Metaphase 1 and 2?
chrom(osomes/atids) randomly orientate, causing independent assortment
73
What happens during Anaphase 1?
chromatids breaks and rejoin at chiasmata to make recombinant chromatids
74
What are pluripotent stem cells?
Those that can form any tissue type but not whole organisms
75
How can you obtain plant stem cells?
From meristem and vascular cambium

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

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