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BIOLOGY AS LEVEL OCR QUESTIONS WITH
VALIDATED ANSWERS
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- CORRECT ANSWER What is cell theory? (2 points)
When the product of a reaction acts as an inhibitor for the enzyme that
produces it
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Cytokinesis is the division of the
cytoplasm where the two cells are produced
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It is in this phase that the
cell is replicating DNA and checking for errors, where mitochondria grow
and divide, and where some of the metabolic processes occur
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S - Synthesis phase, where DNA is replicated in the nucleus
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- CORRECT
ANSWER -Main stages of interphase?

This is the phase where the cell leaves the cycle, either temporarily or
permanently
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The DNA becomes damaged - if DNA becomes damaged, the cell enters a
stage of permanent cell arrest
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It is a lymphocyte, as these leave the cell cycle and can be stimulated to
reenter in an immune response
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Checkpoints - CORRECT ANSWER -What is the name given to the positions in
the cell cycle at which different checks are made before a cell enters another
stage?

- Chromatin fibres coil and condense to form chromosomes
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- Spindle fibres form at either pole of the cell
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This is known as the metaphase plate
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- CORRECT ANSWER -What happens during Anaphase in mitosis?

- The chromatids have reached the poles and the nuclear envelope reforms
around the two new sets of chromosomes
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- In plants, a cleavage furrow cannot form as they have a cell wall
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- CORRECT ANSWER -What happens
during Cytokinesis?

Two genetically identical, diploid daughter cells
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Four genetically different haploid daughter cells
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The first one
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- The nuclear envelope disintegrates
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- The homologous chromosomes pair up, forming bivalents
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- CORRECT ANSWER -Outline the importance
of microscopes in the study of living organisms
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CORRECT ANSWER -Why was cell theory not fully developed before the mid19th century?

1
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2
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3
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4
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- CORRECT
ANSWER -Describe the process of calibrating a microscope
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CORRECT ANSWER -Define magnification
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- CORRECT ANSWER -How does a
compound light microscope work?

A mount used to observe solid specimens, where the specimen is sectioned
and a cover slip is placed over the top
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CORRECT ANSWER -What is a wet mount?

A mount used to observe living specimens where the sample is squashed
gently between the slide and the cover slip
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CORRECT ANSWER -What is a smear slide?

This is used to separate bacteria into gram-positive and gram-negative
bacteria
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Grampositive bacteria retain the dye while gram-negative lose it as they have
thinner cell walls
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This is used to differentiate Mycobacterium from other bacteria
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Mycobacterium retain the stain
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By providing contrast, it allows us to differentiate between cell organelles
that would otherwise be hard to identify
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- CORRECT ANSWER -Define the term 'resolution'
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- CORRECT ANSWER -How does electron microscopy work?

Transmission Electron Microscopy - electrons are transmitted THROUGH
a specimen and focused to produce an image
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CORRECT ANSWER -What is SEM?

Light = inexpensive to buy and operate
Electron = expensive - CORRECT ANSWER -Relative costs of light and electron
microscopes?

Light = small and portable
Electron = large and must be installed - CORRECT ANSWER -Relative
portability of light and electron microscopes?

Light = simple sample preparation that doesn't usually lead to distortion
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CORRECT ANSWER -Relative difficulties of sample preparation of light and
electron microscopes?

Light = natural colour of the sample, or colour of a stain, is seen
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- CORRECT ANSWER -Relative colours of the samples produced from
light and electron microscopes?

Light = up to x2000

Electron = over x500,000 - CORRECT ANSWER -Relative magnifications of
light and electron microscopes?

Light = 200nm
Electron = TEM: 0
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- CORRECT ANSWER -What is an
artefact?

This refers to the chemical reactions of both the synthesis and the breaking
down of molecules
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To contain genetic information in the form of DNA molecules
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- CORRECT ANSWER -What is the function of the nuclear envelope?

To allow molecules, such as mRNA, to move in/out of the nucleus
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Chromatin then coils and condenses to form chromosomes
which only become visible when cells are preparing to divide
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It is a space within the nucleus made of proteins and RNA, and is
responsible for producing ribosomes
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- CORRECT ANSWER
-What are mitochondria?

They have a double membrane, and the inner membrane is folded to form
cristae, which encases the fluid interior known as the matrix
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They are membranous sacs that have important roles in storage and
transportation of substances
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- CORRECT ANSWER -What are lysosomes?

It is a network of fibres necessary for the shape and stability of a cell
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- CORRECT ANSWER -Describe the structure and function
of the cytoskeleton
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Two centrioles form a centrosome, which is
involved in the organisation of the spindle fibres during cell division
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- CORRECT ANSWER
-What are the functions of flagella?

These can move to create a current, causing fluids or objects around the cell
to move
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- CORRECT ANSWER -What is the
function of the smooth endoplasmic reticulum?

To synthesise and transport proteins
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- CORRECT ANSWER -What is the function of
the Golgi apparatus?

Proteins are synthesised on ribosomes bound to the ER
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These
vesicles move due to movement in the cytoskeleton
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Proteins are modified
and packaged into vesicles, before leaving from the Golgi's trans face
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- CORRECT ANSWER -What is the function of the
vacuole?

Tonoplast - CORRECT ANSWER -What is the name given to the membrane
surrounding the vacuole?

They have a double membrane, enclosing fluid inside called stroma
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Stacks of these are referred to as grana, and these contain
chlorophyll
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They only have one molecule of DNA, a chromosome, and this is supercoiled to make it more compact
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- CORRECT ANSWER -How is the DNA in a prokaryotic cell packaged?

Smaller in prokaryotes
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Nerve impulse transmission
2
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Nerve impulse transmission
2
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Nerve impulse transmission
2
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Catalyse reactions
2
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- CORRECT ANSWER -Roles of chloride ions (1)

1
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Nucleic acid and ATP formation
3
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Catalyse reactions
2
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- CORRECT ANSWER -Define the term 'polymer'
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CORRECT ANSWER -Why does water have a much higher boiling point than
expected?

Solid water (ice) is less dense than water in its liquid state
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- CORRECT ANSWER -Describe an
unusual property of water?

Cohesion
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Polarity
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- CORRECT ANSWER -Which two properties allow
water to exhibit capillary action: the process by which water is able to rise
up a narrow tube against the force of gravity?

The hydrogen bonds between the molecules, as it takes a lot of energy to
overcome these forces
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It maintains a constant temperature in cellular environments, providing
the correct environment for enzymes to function
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It provides a stable habitat for aquatic animals
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Carbon 1 and 4 - CORRECT ANSWER -Between which carbon atoms does a
reaction take place when two glucose molecules bond?

Glycosidic
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- CORRECT ANSWER -Glucose + Glucose = __________

Sucrose
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- CORRECT ANSWER -Glucose + Galactose = _________

Sweeteners
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- CORRECT ANSWER -What is starch?

Amylose and amylopectin
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These bond angles force the chain to twist into a helix, which is
stabilised by hydrogen bonding in the molecule
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This gives it a
branched structure
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- CORRECT ANSWER -What is an animal's equivalent of starch?

It means that the molecule can be more compact, and so they can be stored
when the animal is mobile
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-

CORRECT ANSWER -What advantages do the additional branches on glycogen

have to the animal?

Hydrolysis
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- CORRECT ANSWER -Glycogen and starch are formed from molecules
of ______ glucose
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- CORRECT ANSWER -Cellulose is formed from molecules of ______
glucose
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- CORRECT ANSWER -What is different about the
reaction between two beta glucose molecules (as opposed to two alpha
molecules)?

A straight (unbranched) chain molecule - cellulose
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These then join together to form __________, which join to produce
________ which are strong and insoluble, and are used to make cell walls
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Place liquid form of sample into boiling tube
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Add an equal volume of Benedicts reagent
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Heat the mixture in a water bath for 5 minutes
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If ____ is present, the solution will change from blue to brick-red
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This REDUCES (reduction = gain of electrons)
them from blue Cu2+ to brick-red Cu+ ions
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- CORRECT ANSWER -________ is the most common non-reducing
sugar
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Boil sample with dilute hydrochloric acid
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Add an equal volume of Benedict's reagent
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Heat the mixture in a water bath for 5 minutes
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If ____ is present, the solution will change from blue to brick-red
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- CORRECT ANSWER -Why does boiling with
hydrochloric acid change the outcome for non-reducing sugars in the
Benedict's test?

1
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2
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- CORRECT ANSWER -How to test for starch?

1
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2
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3
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4
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5
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6
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- CORRECT ANSWER Quantitative way to determine concentration?

Fats are typically solid at room temperature while oils are typically liquid
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The bonds formed are _______ bonds
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- CORRECT ANSWER -Esterification is a
type of _____________ reaction, and so triglycerides can be broken into
their components through the addition of _____ ________
____________
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- CORRECT ANSWER -What
is a saturated fatty acid?

- CORRECT ANSWER -Structure of a fatty acid?

A fatty acid with one double bond between the carbon atoms
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CORRECT ANSWER -What is a polyunsaturated fatty acid?

Bend, which means that they cannot pack as closely together, making them
liquid at room temperature instead of solid
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Hydrophilic heads go into the water whilst the hydrophobic tails remain
sticking out, forming a layer on the surface of the water
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This enables them to form a membrane which can
separate the aqueous environment of cells from the aqueous cytosol within
cells
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- CORRECT ANSWER -Which part of a sterol is
hydrophilic?

It helps to form cell membranes, and positions itself between the
phospholipids to provide stability and regulate their fluidity
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Membranes - hydrophobic barriers - CORRECT ANSWER -Lipids can form
_________ and __________ __________

Hormones
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Electrical insulation - nerve impulse transmission
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Thermal insulation - heat loss
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Cushion vital organs
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Buoyancy
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1
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2
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3
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CORRECT ANSWER -Test for lipids?

Lipids are not soluble in water, but are soluble in ethanol, and so the lipid
can dissolve into ethanol
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- CORRECT ANSWER -How
does the emulsion test work?

A polymer made up of amino acid monomers
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- CORRECT ANSWER -Which groups on the amino acids react to form
a peptide bond + water?

Hydrogen bonds
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Which is the weakest type of bond that can form between R
groups?

Disulfide bonds - covalent bonds that form between R-groups containing
sulfur atoms
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Which is the strongest type of bond that can form between R groups?

Ionic bonds
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Which type of bond forms between oppositely charged R-groups?

Hydrophobic and hydrophilic interactions
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Which type of bond forms between
polar and non-polar R-groups?

The sequence in which the amino acids are joined
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- CORRECT ANSWER -What is the secondary structure of a
protein referring to?

This refers to the folding of the protein into its final shape, and is where the
R-groups begin to interact
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Interactions between the subunits are the same as in the tertiary
structure, except that they form between different protein molecules
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Mix liquid sample with sodium hydroxide solution
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Add copper sulfate solution until the mixture turns blue
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Leave to stand
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If peptide bonds are present, then the solution will turn from blue to
violet
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An
example would be insulin, which is involved in the regulation of blood
glucose concentration
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Haemoglobin is an example, as it is formed
from four protein subunits, each wrapped around a haem group
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- CORRECT ANSWER -What are conjugated
proteins?

Conjugated
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These are formed from long, insoluble molecules
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Examples include keratin, which contains
cysteine, elastin, which is found in the walls of blood vessels, and collagen a connective tissue found in skin, tendons and ligaments
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Include
DNA and RNA
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A long sugar-phosphate 'backbone' with a base attached to each sugar
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4 - adenine, cytosine, guanine and thymine
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These are
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Larger - double - CORRECT ANSWER -Purine bases are ________ and contain
______ carbon ring structures
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- CORRECT ANSWER -The two DNA pyrimidine bases are _______
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- CORRECT ANSWER -The two DNA purine bases are ______
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- CORRECT ANSWER -Why can't C pair with T?

Because these are both purine bases and bonds can only form between one
purine and one pyrimidine
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- CORRECT ANSWER -What type of bonds hold the two
strands of DNA together?

Antiparallel
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It also ensures that there is always equal amounts
of A and T, and equal amounts of C and G
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The pentose sugar is ribose, rather than deoxyribose
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Thymine has been replaced with Uracil
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Grind sample in mortar and pestle to break down the cell walls
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Mix sample with detergent to break down the cell membrane
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Add salt to break the hydrogen bonds between the DNA and water
molecules
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Add protease, to break down the proteins associated with DNA
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Add a layer of alcohol gently on top of the sample, causing the DNA to
precipitate out of solution
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DNA is seen as white strands between the alcohol and the sample
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This is the process where one molecule of DNA replicates into two new
ones, and each new molecule has one strand from the original DNA
molecule, and one strand made up of free DNA nucleotides
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DNA helicase
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- CORRECT ANSWER -Which is the enzyme that catalyses the
formation of phosphodiester bonds between the nucleotides?

Mutations
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- CORRECT ANSWER -There are 64
different base codons possible, but only 20 amino acids that regularly occur
in biological proteins
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Translation - CORRECT ANSWER -____________ is the second stage in
protein synthesis
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- CORRECT ANSWER -During protein synthesis, the
double helix structure unwinds due to the action of _______
___________, beginning at a ________ _______
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DNA nucleotides - phosphodiester - CORRECT ANSWER -In transcription, after
the DNA has unzipped, free ___ _________ pair with the complementary
base pairs and join together with _____________ bonds
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Translation - ribosome - CORRECT ANSWER -___________ begins when the
RNA binds to a ___________
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tRNA - anticodon - codon - CORRECT ANSWER -In translation, the end of the
________ has an ___________ which binds to the complementary
_______ on the strand of mRNA
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Amino acids - peptide - CORRECT ANSWER -In translation, the sequence of
______ _______ join together by _______ bonds, gradually forming a
polypeptide
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- CORRECT ANSWER -ATP is the
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- CORRECT ANSWER -How does ATP release
energy?

Small molecule - CORRECT ANSWER -Property of ATP that enables it to move
easily in/out of cells?

Water soluble - CORRECT ANSWER -Property of ATP that enables it to provide
energy in aqueous environments?

It's large enough to be useful, but not so large so that energy is wasted as
heat
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- CORRECT ANSWER -Property of ATP
that prevents energy being wasted as heat?

Each enzyme is specific to a particular substrate, and so there is an area
within the tertiary structure of the enzyme that has a shape complementary
to the substrate, known as the active site
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This
leaves the enzyme unchanged and able to take part in subsequent reactions
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This states that the active site of the enzyme changes slightly as the
substrate enters
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This strain can then weaken
bonds in the substrate, lowering the activation energy required for the
reaction
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The energy required to start a reaction
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A measure of how much the rate of reaction increases with a 10 degree rise
in temperature
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- CORRECT ANSWER -Define the term 'denatured' with reference to
enzymes
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As the enzyme cannot carry out its function, it is
said to be inhibited
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CORRECT ANSWER -What is competitive inhibition?

A molecule binds to the enzyme at a site other than the active site (known
as an ALLOSTERIC site)
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When the
active site changes shape, it is no longer able to bind to the complementary

substrate, and so the enzyme cannot carry out its function
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- The orientation of each homologous pair is random and so this leads to
independent assortment, as any alleles can be made facing the poles
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-Sections of DNA on sister chromatids can detach and become entangled
during crossing over, sometimes resulting in the exchange of DNA
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- When sections of DNA are swapped, recombinant chromatids are formed,
resulting in genetic variation
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- Nuclear membrane reforms
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- Cytokinesis
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- In each cell, the nuclear envelope breaks down and spindle formation
begins
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- Due to crossing over, the chromatids are no longer identical so there is
more independent assortment happening here
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- CORRECT ANSWER -What
happens during Anaphase 2 in Meiosis 2?

- The chromatids assemble at the poles and the chromosomes uncoil and
form chromatin again
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- Nucleolus becomes visible
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CORRECT ANSWER -What happens during Telophase 2 in Meiosis 2?

- Large SA:V ratio for maximum oxygen uptake
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- No nucleus/ organelles, so more room for haemoglobin
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- CORRECT ANSWER -How
are erythrocytes adapted to their function?

Approximately 90 days
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- Many lysosomes, containing enzymes for hydrolysis of pathogens
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- Many mitochondria for ATP
- Many Golgi for production of lysosomes
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- CORRECT
ANSWER -How are neutrophils adapted to their function of defending the
body against disease?

- They have an acrosome, which contains digestive enzymes to penetrate
the protective layer around the ovum
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- Many mitochondria to provide ATP for movement of flagella
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- Squamous (flattened) to give a short diffusion pathway
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- CORRECT ANSWER -How are epithelial
cells adapted to their function?

- Many mobile chloroplasts to absorb light energy and provide ATP
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- Large vacuole pushes chloroplasts to the edges of the cell
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- CORRECT ANSWER How are palisade cells adapted to their function in plants?

- They have extensions which enable them to get deeper into the soil
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- Mitochondria provide ATP to enable the movement of mineral ions by
active transport
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-Thicker inner cell walls force the guard cells to bend outwards
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CORRECT ANSWER -How are guard cells adapted to their function of taking in
water in plants?

- They are very thin to allow for rapid diffusion across a surface
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CORRECT ANSWER -How is the tissue squamous epithelium adapted to its
function of covering body surfaces?

- They have cilia on the top to move mucus
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- CORRECT
ANSWER -How is the tissue ciliated epithelium adapted to its function?

- It contains fibres of elastin and collagen, which increases its flexibility
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- CORRECT ANSWER -How is the tissue cartilage
adapted to its function?

- Contain myofibrils (which contain contractile proteins) to enable the
tissue to contract and move the bone
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- It is usually covered by a waxy cuticle to reduce the loss of water
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- CORRECT ANSWER -How is the
epidermis tissue adapted to its function in plants?

- It is composed of vessel elements, which are long and thin dead cells
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- CORRECT ANSWER -How is the xylem tissue
adapted for its function in the transportation of water and minerals through
a plant?

- It is composed of columns of sieve tube cells and parenchyma cells (used
for food storage)
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- Has many mitochondria as it is required to use active transport
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- CORRECT ANSWER -What is
the definition of a tissue?

A collection of specialised tissues that are adapted to work together to
perform a particular function
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- CORRECT ANSWER -What is the
definition of a stem cell?

Its ability to differentiate into different types of cell
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Examples include a
zygote, and the first 8 to 16 cells of its mitotic divisions
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They are present in early embryos
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Haematopoetic stem cells in bone marrow can differentiate into various
types of blood cell
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- Tissue (adult) stem cells are present through life from birth
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- Umbilical cords of newborn babies
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- CORRECT ANSWER -Sources
of plant stem cells?

- Heart disease: heart attacks can cause permanent damage to muscle tissue
in the heart
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- Parkinson's: symptoms caused by death of dopamine-producing cells, so
stem cells could help this
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- Spinal injuries: Stem cell implants could help to repair damaged spinal
cords
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- Treatment of burns: Stem cells grown on mesh can provide new skin for
burn patients
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- Developmental biology: This can help to show scientists more about what
happens as organisms grow and develop from a single cell, and why some
things go wrong
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