Nayland College Level 2 Biology – External Exam Notes!
AS 91156 Demonstrate Understanding
of life processes at the cellular level
What you
need to do
guide!
To get bronze (achieved)…
You will need to clearly show the examiner that you understand (definitions, using annotated diagrams or
models to describe, and describing characteristics of, or providing an account of)
life processes at the
cellular level.
To go for silver (merit)
You will need to demonstrate in-depth understanding (use biological ideas to give reasons how or why) of life
processes occur at the cellular level.
And the gold medal (excellence) goes to the student that:
Demonstrates a comprehensive understanding (linking biological ideas) about life processes at the cellular
level. Your answers should include: justifying, relating, evaluating, comparing and contrasting and analysing.
Life processes at the cellular level include:
 photosynthesis
 respiration
 cell division (DNA replication and mitosis as part of the cell cycle).
Biological ideas, as they relate to each of the life processes at the cellular level, will be selected from:
 movement of materials (including diffusion, osmosis, active transport)
 enzyme activity (specific names of enzymes are not required)
 factors affecting the process
 details of the processes only as they relate to the overall functioning of the cell (specific names of stages
are not required)
 reasons for similarities and differences between cells such as cell size and shape, and type and number of
organelles present.
Cells include plant cells and animal cells.


Rules of the game
There will probably be three questions. Each question will focus on a physical factors and an associated
technique.
You will have 3 hours to do 3
papers, which gives you 60 mins per paper! Heaps of time to plan your answer and check you have read
the question correctly
The 2013 exam specs give us some clues on what the 3 questions will be. It is LIKELY the questions will be:
There will probably be a question on DNA structure and semi- conservative replication
Understanding of the structure of DNA, and the meaning of semi-conservative replication as part of
cell division, is expected.
There may be a question on how environmental factors affect photosynthesis and enzyme activity
Factors affecting the processes may include the direct availability of resources (e.g. sunlight, water,
CO2 are all needed for photosynthesis) as well as the indirect effect of factors that affect enzyme
activity within cells (e.g. temperature, pH, substrate, concentration, co-enzymes, enzyme poisons).
Another question probably on: how similarities and differences between cells may relate to the overall
functioning of the organism and justifying the reasons for these similarities and differences.
DNA structure and semi-conservative replication
Concept
DNA structure
DNA Replication
Key sentences
DNA is a double helix molecule
Made of 4 nucleotides (A, T C,G)
The sequence of nucleotides determines the genetic code
Each Nucleotide made of a deoxyribose sugar, base and phosphate
The sugar and phosphate are identical on all DNA nucleotides
The base determines which nucleotide it is (A,G,T,C)
The DNA molecule has a 5’ and a 3’ end (‘ = prime)
Base pairing rule: A pairs with T, C pairs with G.
One DNA strand runs 5’ to 3’, the other strand runs 3’ to 5’, this is called an
antiparallel structure
Two enzymes involved are: Helicase, DNA Polymerase
Replication fork is formed (helicase unwinds (unzips) the DNA)
During replication, multiple replication forks are formed, replication happens in
both directions, this speeds up replication
Free nucleotides are added to the 3’ of the new strand by DNA polymerase
One strand is the leading strand
One strand is the lagging strand
Okazaki fragments form on the lagging strand
Semi-conservative
replication
Two new DNA molecules are formed
Each new DNA molecule is made up of one strand of the original DNA, this is
called semi-conservative replication.
Semi-conservative replication improves the accuracy of the replication process.
The nucleotides sequence on the newly formed strand can be checked against
the nucleotide sequence on the original strand
Why Replicate
All organisms must undertake cell division
Cell division is needed for growth, repair and reproduction
DNA replication happens in both mitosis and meiosis
A complete copy of the DNA is needed in each new cell formed.
DNA contains the instructions for all essential cellular processes
Cell structure and Function
Concept
Chloroplast
Cell parts (organelles)
Mitochondria
Plasma
membrane
Vacuoles
Cell wall
Golgi Bodies
Cell shape and size
Structure in relation
to photosynthesis
Structure in relation
to respiration
Key sentences
Site of Photosynthesis
Substrates: CO2 and water
Products: Glucose and O2 (O2 = waste product)
Contains a chemical called chlorophyll
Found in the upper/ outer tissues where sunlight can penetrate
Site of (aerobic) Respiration
Converts glucose (and other foods) into ATP
Require – glucose and O2
Waste products – CO2 and H2O
Semi-permeable
Allows small molecules through but not large ones (glucose yes, starch no). Gases
go through by diffusion.
Water goes through by osmosis.
Bigger molecules can pass across the membrane via active transport (uses
energy). This is controlled by the cell using proteins embedded in the membrane.
Plasma membranes may have small fold called microvilli
In plants – vacuoles are large and take up whole centre of mature cell. Used to
store carbohydrates
In unicellular animals – contractile vacuoles used to regulate osmosis and food
vacuoles created with food is engulfed into a vacuole (phagocytosis)
Plant cells only. Strong and slightly elastic.
Completely permeable (everything goes through).
Transport vesicles. Carry proteins (made in the ER) to the edge of the cell
Vesicles fuse with plasma membrane and release contents extra-cellular
Cell shape effects the rate of diffusion in and out of the cell
Cell size effects the rate of diffusion into the centre of the cell
An oblong cell has a bigger surface area than a cubed cell
A large cell will take longer for particles to reach the centre of the cell than a small
cell
Increasing the surface to volume ratio will increase the rate of passive transport.
Microvilli are folds in the plasma membrane that greatly increase its surface area.
When illuminated with light plant cells containing chloroplasts undertake
photosynthesis. (All plant cells undertake respiration all the time).
Substrates: CO2 and water. Products: Glucose and O2
Cells undertaking p/s need to be able to undertake gas exchange.
A large surface/ volume ratio improves diffusion of CO2 in and O2 out.
All living cells undertake respiration all the time
The more energy a cell needs the more mitochondria. (muscle cells)
O2 and glucose need to diffuse into the cell
CO2 needs to diffuse out of the cell
If O2 is insufficient, the electron transport chain stops, the kerb cycle stops and
anaerobic respiration starts
Key diagrams for cell structure and function
Some words to use
http://leavingbio.net/photosynthesis.htm
http://crescentok.com/staff/jaskew/isr/biology/eoi/eoi.htm
http://www.mrothery.co.uk/exchange/exchange.htm
http://physicsmadeeasy.wordpress.com/biology-notes/cell-structure-and-function/
Active Transport
 Cell Membrane
 Cell Wall
 Cellular Respiration
 Chloroplast
 Cilia
Concentration Gradient
 Cytoplasm
 Diffusion
 Flaccid
 Induced Fit Model
 Ion Exchange Pump
 Light Dependent
Reaction
Light Independent
Reaction
 Mitochondria
 Organelles
 Osmoregulation
 Osmosis
Passive Transport
 Phagocytosis
 Photosynthesis
 Semi-Permeable
Membrane
 Substrate
 Surface Area : Volume
Ratio
 Vacuole

Enzyme Activity and Environmental factors
Environmental
factors on enzymes
As temp increases, the kinetic energy of the molecules increases and collisions
between substrates and enzymes increase.
As temp decreases, the kinetic energy of the molecules decreases and collisions
between substrates and enzymes decreases.
However, when temp reaches a critical temp, the enzyme changes its 3D
structure (denatured) (due to the kinetic energy breaking the hydrogen bonds),
and the active site of the enzyme becomes ineffective
pH – When an enzyme is outside of its optimum pH (too high or too low) the
enzyme denatures (changes its 3D structure) and the active site becomes
ineffective
Most enzymes have an optimum pH of 7 (neutral).
As substrate concn increases, the rate of enzyme activity increases.
As substrate concn decreases, the rate of enzyme activity decreases.
Increasing substrate concn increases the kinetic energy of the molecules and the
number of collisions between substrate and enzyme.
Environmental
factors on the rate of
photosynthesis
Temp increases the rate of p/s
Substrate concentration (CO2 or water)increases the rate of p/s
Environmental
factors on the rate of
respiration
Temp increases the rate of resp
Substrate concentration (O2 or glucose)increases the rate of resp
Key diagrams