Download Cell Biology - Revision Notes

St Ninian’s High School
Biology Department
National 5
Unit 1: Cell Biology Summary Notes
Name: _______________________
Cell Ultra Structure
A cell is the basic unit of life.
There are 4 main types of cells to learn in National 5 Biology.
Animal Cells
Animal cell has 5 key parts.
Ribosomes
Mitochondria
Cytoplasm
Nucleus
Cell membrane
Plant Cells
Plant cell has 8 key parts.
Vacuole
Cytoplasm
Hint!
Don't get mitochondria and chloroplasts
confused!
Mitochondria = wiggly line in middle
Chloroplast
Chloroplast = stacks of discs
Mitochondria
Nucleus
Ribosomes
Cell wall
Cell membrane
Cell Ultra Structure
Yeast Cell
Yeast cell has 7 key parts.
Ribosomes
Mitochondria
Cell wall
Vacuole
Cell membrane
Cytoplasm
Nucleus
Bacterial Cell
Bacterial cell has 6 key parts.
Plasmid
Ribosomes
Cytoplasm
Cell membrane
Cell wall
Free-floating
DNA
Cell Ultra Structure
Cell Part
Function
Cells
Ribosomes
Site of protein synthesis
All
Cytoplasm
Where chemical reactions
occur
All
Cell membrane
Controls what enters and
leaves the cell
All
Nucleus
Controls all cell activities
Animal, plant and yeast
Mitochondria
Site of aerobic respiration
Animal, plant and yeast
Cell wall
Supports the cell
Plant, bacteria and yeast
Vacuole
Stores cell sap
Plant and yeast
Chloroplasts
Site of photosynthesis
Plants only
Plasmids
Passed naturally between
bacteria. Extra circular
piece of DNA.
Bacteria only
Free floating DNA
Genetic material that
codes for protein
Bacteria only
Cell Microscope Calculation
Calculate the average length of the cells in micrometres.
(1mm = 1000 micrometres)
10 mm divided by 5 cells = 2mm per cell
Convert mm into micrometres.
2 x 1000 = 2000 micrometres
10mm
length
Remember...
width
Cell Membrane
Function of the membrane
Controls what enters and leaves the cell.
Selectively permeable
Only allows small molecules to move in and out of cell, but NOT large molecules.
Small molecules
Oxygen
Water
Carbon dioxide
Glucose
Amino acids
Fatty acids and glycerol
Large Molecules
Proteins
Fat
Starch
Large molecules require to be digested by enzymes before they can pass through the
membrane.
Proteins
Structures in the membrane
1.
Phospholipids
2.
Protein
Phospholipids
Transport across the Membrane
Molecules can move across the membrane in TWO ways.
1.
2.
Passive transport (diffusion and osmosis)

High to low concentration (down the concentration gradient).

No energy required.

Very slow process due to no energy needed.
Active Transport

Low to high concentration (against concentration gradient).

Energy required to allow membrane proteins to
move molecules from low to high concentration.
Importance of Diffusion in everyday life

Oxygen/glucose diffuse INTO cells for
respiration.

Carbon dioxide & water diffuse OUT of cells as waste products produced
by respiration.
Osmosis in Cells
Animal Cells
Animal cells are surrounded only by the membrane, therefore they either burst or
shrink depending on their surrounding solutions.
Pure Water
Salt/Sugar Water
HWC
HWC
LWC
LWC
Animal cells will gain mass.
Animal cells will lose mass.
Cell will SWELL & BURST.
Cell will SHRINK.
Plant Cells
Plant cells are surrounded by a cell wall which prevents cell bursting or shrinking.
Pure Water
Salt/Sugar Water
Turgid plant cell
1. Vacuole gets bigger (stores water).
2. Cell membrane pushes against the
cell wall.
Plasmolysed plant cell
1. Vacuole gets smaller (loses water).
2. Cell membrane pulls away from the
cell wall.
Summary of Animal/Plant Cells
Type of Cell
Strong Salt Solution
Pure water
Animal
Shrink
Burst
Plant
Plasmolysed
Turgid
Osmosis Problem Solving
What is osmosis?
A special case of diffusion involving water molecules.
Water molecules move from areas of high WATER concentration to areas
of low WATER concentration through a selectively permeable membrane.
Osmosis In Cells
Cell placed in pure water;
Cell placed in strong salt/sugar solution;

Gain mass

Lose mass

High water concentration outside the
cell to low water concentration inside
the cell

High water concentration inside the
cell to low water concentration
outside the cell
*****Likely 2 mark exam question*****
Q. Explain what happens to the following cells in terms of water movement.
A
Pure water
Water moves into the cell by osmosis
(1 mark)
from an area of high water concentration
outside the cell to an area of low water
concentration inside the cell
(1 mark).
B
Strong salt
solution
Water moves out of the cell by osmosis
(1 mark)
from an area of high water concentration
inside the cell to an area of low water
concentration outside the cell
(1 mark).
Hint! Think....where’s the high water concentration, where’s the low water
concentration.
Osmosis Problem Solving
Possible exam question
Q. Why should you blot the plant tissue dry before starting an osmosis experiment?
A.
Blotting tissue sample prevents excess/ external water being taken into account.
Problem Solving
Calculating percentage change (also called percentage increase/decrease)
change
X 100
original
Worked Examples
1.
A plant cell is placed in pure water.
The plant cell weighed 12g before, and now weighs 15g after osmosis has
occurred. Calculate the percentage change in mass.
Change = 15-12g = 3g
Original number = 12g
(3÷12) x 100 = 25%
2.
A plant cell was placed in a 20% salt solution, and as a results now weighs 4g.
If the plant cell originally weighed 10g, calculate the percentage change in mass.
Change = 10-4g = 6g
Original number = 10g
(6÷10) x 100 = 60%
Mitosis
What is mitosis?
When 1 diploid cell produces two identical diploid cells.
Mitosis maintains diploid chromosome number.
Diploid = 2 matching
sets of chromosomes
46
46
46
46
46
46
46
Why undergo mitosis?

Single celled organisms – reproduction.

Multicellular organisms - growth & repair.
Location of mitosis
In the nucleus (DNA found here)
***Importance of maintaining the number of chromosomes (complement)***
To ensure no genetic information is lost.
Mitosis
Long uncoiled chromosome, not yet visible.
Nuclear membrane breaks down.
Chromosomes replicate to form 2 chromatids.
Chromosomes are now visible.
Chromosomes line up at the equator (middle) of
the cell and spindle fibres attach
(at centromere).
Chromatids pulled to opposite poles (ends) of
cell by spindle fibres.
Nuclear membrane reforms .
Cytoplasm divides.
2 identical diploid daughter cells are
produced.
Aseptic Technique
Aseptic Technique
Promote cell division (growth) of 1 microorganism by preventing contamination by
other micro organisms.
Techniques used
1. Disinfecting working areas
2. Washing hands
3. Use of lab coats
4. Flaming bottle necks in a Bunsen burner
Industrial fermenters
Containers used to grow micro organisms on a large scale to make useful products
such as beer, wine or antibiotics.
Fermenters need to control ABIOTIC factors to ensure optimum bacterial growth.
These factors include;

Temperature

Oxygen concentration

pH
DNA Structure
Location of DNA
DNA is found in the nucleus of the cell.
DNA molecules are made up of nucleotides which have 3 basic parts.
phosphate
base
sugar
Structure of DNA
The 2 strands of DNA nucleotides are held together in a twisted
3D structure known as a double helix.
DNA Bases
DNA has four different bases which form complementary base pairs as follows,
making up the GENETIC CODE.
Adenine (A)
Thymine (T)
+
Guanine (G)
Cytosine (C)
+
Complementary base code example
A G T C A G C T (Strand 1)
T C A G T C
G A (complementary strand 2)
DNA Calculations
DNA Calculations
Your exam paper may ask you to calculate the percentage of A bases given the number
of G bases etc.
Two worked examples are shown below.
Worked example 1
If there are 1200 bases in total and 300 are adenine (A) – how many are cytosine (C)?
A - 300
= T – 300
G + C = 1200 – 600 = 600 bases for both G + C
Therefore, G = 600/2 = 300 bases
Worked example 2
If 10% of 4000 bases are thymine (T), what number are guanine (G)?
T - 10% = A - 10%
G + C = 80% divide by 2 = 40% are G
Now find 40% of the total (4000)
40/100 X 4000 = 1600 bases
DNA Function
Function of DNA
DNA is a genetic code for protein.
The Genetic Code
A particular protein is made by a particular amino acid sequence, which is determined
by the original DNA base sequence (genetic code).
Base Sequence
(determines)
Amino Acid sequence
(determines)
Protein structure
(determines)
Protein function
Making Proteins
DNA cannot leave the nucleus to take the genetic code to the ribosomes to make
proteins. Therefore, it makes a single stranded copy of the genetic code which can
travel to the ribosomes. This messenger molecule is called mRNA.
mRNA (messenger RNA)

mRNA is produced in the nucleus from complementary base pairing with one of the
two DNA strands.

mRNA is identical to DNA except its 4 bases are:
A&U
C&G
mRNA function
Takes complementary genetic code from the nucleus to the ribosomes.
mRNA
DNA
A
G
T
C
U
C
A
G
T
C
A
G
A U
T
mRNA leaves the nucleus and
travels through the cytoplasm
to the ribosome
DNA
mRNA
U
G
A
ribosome
DNA
DNA vs. mRNA
DNA
mRNA
Double stranded
Single stranded
Bases = C & G A & T
Bases = C & G
A&U
C
U
Making Proteins
Ribosomes
Once mRNA attaches onto the ribosomes, 3 bases = 1 specific amino acids.
This forms a specific amino acid sequence making a specific protein.
Different types of protein
Proteins are made up of different sequences of amino acids.
The different amino acid sequences fold the protein into different shapes giving it
a different STRUCTURE and therefore a different FUNCTION.
Type of Protein
Enzyme
Function
Speeds up chemical reactions inside cells.
Antibodies
Fight disease/infections by bacteria.
Receptors
Bind to specific hormones at target tissue.
Structural
Provides support.
Hormone
Chemical messengers that travel in blood from one
place to another.
Enzymes
Enzymes are biological catalysts
They speed up reactions but are not used up in the reaction.
Importance of Enzymes
Enzymes allow reactions to happen at relatively low temperatures (37 °C).
Lock & Key Theory
Enzymes interact with substrate molecules at the enzyme’s active site to produce a
product.
(substrate)
(products)
(substrate fits into enzyme’s
active site)
(enzyme)
The active site is uniquely shaped that only fits 1 type of substrate (lock & key model).
Factors affecting enzyme activity
1.
Temperature
2.
pH
Enzymes
Enzyme activity with temperature graph
Optimum temperature
The optimum temperature is the temperature where the enzyme works best.
Every enzyme has the same optimum temperature of 37°C.
Denatured Enzymes
Above 40°C the active site of the enzyme is permanently damaged and the enzyme no
longer works. The enzyme is said to be denatured.
(normal enzyme)
(denatured enzyme)
Top tip
At low temperatures enzymes do not work very well but they are NOT denatured.
This is because if the temperature is increased to the optimum the enzyme will work
well again.
Enzymes
pH
The pH scale is a measure of the hydrogen ion concentration and is given a rating 1-14.
Acid pH = 1-6
Neutral pH = 7
Alkali pH = 8-14
Enzyme activity with pH graph
Different enzymes work best at different pH values, their optimum pH.
Many enzymes’ optimum pH is neutral (pH 7) but not all!
Pepsin optimum – pH 2
Amylase optimum – pH 7
Pepsin
amylase
2
Catalase optimum – pH 9
catalase
7
Enzyme activity
9
1
2
3
4
5
6
7
8
9
10
11
12
pH
Denaturing & pH
Extremes of pH (strong acid/alkali) can denature the active site of an enzyme, causing
the enzyme to become inactive.
Enzymes
2 types of enzyme reactions;
Degrading reactions
1 large substrate is broken down into smaller products i.e. during digestion
substrate
enzyme
product
Substrate
Enzyme
Product
Hint?
Hydrogen Peroxide
Catalase (liver)
Water + oxygen
HPCOW
Starch
Amylase (saliva)
Maltose
SAM
Protein
Pepsin (stomach)
Amino Acids
PPAA
Fat
Lipase
Fatty acids &
glycerol
FLAG
Synthesising Reaction
1 small substrate is joined together to make a larger product.
substrate
enzyme
product
Substrate
Enzyme
Product
Hint?
Glucose-1-phosphate
Phosphorylase
Starch
G1PPS
Phosphorylase only found in plants which stores glucose made during photosynthesis
as starch.
Genetic Engineering
Bacterial Plasmids
Bacteria transfer plasmids in two ways;
1. Naturally between bacteria
- to pass on a specific advantage between bacteria through sharing plasmids
e.g. passing on resistance to antibiotics
2. Genetic engineering of bacteria
- a gene from an animal/plant is inserted into the bacterial plasmid to produce the
foreign protein in the bacterial cell.
Why use bacteria as the host cell?
1. Bacterial cells divide quickly by mitosis.
2. DNA found loose in cytoplasm, easy to modify.
Plasmid
Free-floating
DNA
***Likely problem solving question***
A bacterial cell replicates every 2 minutes.
Calculate how many bacterial cells are present after 12 minutes?
O mins – 1 bacterium
2 mins – 2 bacteria
4 mins – 4 bacteria
6 mins – 8 bacteria
8 mins – 16 bacteria
10 mins – 32 bacteria
12 mins – 64 bacteria
Genetic Engineering
Examples of genetically engineered products

Insulin for the control of diabetes.

Antibiotics such as penicillin to kill bacteria.

Growth hormone for dwarfism.
Stages of genetic engineering
1.
The insulin gene is ‘cut out’ from a human chromosome using enzymes.
2.
The plasmid is removed from the bacterial cell and is ‘cut open’ using enzymes.
3.
The insulin gene is then inserted into the plasmid which is then put back into
a new bacterial cell.
4.
The modified bacterial cell is then added to a fermenter, where it divides and
produces insulin in large quantities.
5.
The insulin produced by bacterial is continually collected and purified.
Genetic Engineering
Advantage of genetic engineering
Can produce large quantities of substances that were difficult to obtain previously.
Disadvantage of genetic engineering
Controversial as concerns over;
1.
GM bacteria passing on antibiotic resistance to other bacteria in the outside
environment.
2.
GM crops can pass on weedkiller resistance to weeds.
Photosynthesis
Word Equation
LIGHT ENERGY
carbon dioxide + water
(raw materials)
Photosynthesis
1.
oxygen
(by-product)
CHLOROPHYLL
+ glucose
(carbohydrate
food product)
is a complex series of enzyme controlled steps split into TWO stages;
Light Dependent Stage
2.
Carbon Fixation
Light Dependent Stage
Using light energy to
a)
Join ADP and Pi using light energy to make ATP (chemical energy) which is
needed for Carbon Fixation.
b)
Splitting up water (photolysis) into oxygen (by-product) and hydrogen which is
needed for Carbon Fixation.
(needed for stage 2)
Photosynthesis
Energy Conversion
Light energy is absorbed by chlorophyll in chloroplasts.
The light energy is converted into chemical energy as ATP to be used in
Carbon Fixation.
Hydrogen & ATP made in Light Dependent Stage taken to Carbon Fixation stage.
Carbon Fixation
Carbon Fixation consists of several enzyme-controlled reactions which take the form
of a cycle.
The cycle forms glucose from carbon dioxide by adding hydrogen and ATP from the
Light Dependent stage.
ATP + Enzymes
Fates of glucose made during Carbon Fixation
Glucose
(for respiration)
Starch
(storage carbohydrate
in leaves)
Iodine turns black when starch is present.
Cellulose
(structural carbohydrate in cell
walls in plants ONLY)
Photosynthesis—Limiting Factors
A limiting factor is simply anything that if increased, increases the rate of
photosynthesis.
Rate of photosynthesis (units)
Photosynthesis has
Light Intensity
limiting
30
3 limiting factors:
Light Intensity
no longer limiting

Temperature
10

Light intensity
0

Carbon dioxide concentration
20
0
10
20
Light Intensity (units)
Limiting factors—worked example
30°C
25% CO2 conc.
C
30°C
15% CO2 conc.
B
20°C
15% CO2 conc.
A
Hints!
If the line is going up, look down to the bottom axis.
If the line is going across, look up to the next line, what’s changed?
Limiting factor at points;
A = light intensity
B = temperature
C = carbon dioxide concentration
Measuring Photosynthesis
Testing Leaf for Starch
Plants can be checked to see if they are photosynthesising if they are producing starch
in their leaves by using iodine which turns black in presence of starch.
Only green leaves that have been placed in the following conditions will produce
starch.
1.
Plentiful light
2.
CO2 present
3.
Room temperature
(enzymes near their optimum)
Measuring the rate of photosynthesis
The rate of photosynthesis can be measured by using a pond weed such as elodea.
The beaker contains water full of carbon dioxide, with a lamp used to provide light.
A heat shield is used to provide the plant overheating and affecting results.
The number of oxygen bubbles per minute is then measured.
ATP
ATP is made up of one adenosine molecule and 3 phosphates (Pi).
ATP is made from ADP and Pi.
Function of ATP
ATP is a high energy molecule that transfers CHEMICAL energy from respiration to
reactions that require ATP, such as;
Protein synthesis (in ribosomes)
Muscle contraction
Active transport
Aerobic Respiration
The chemical energy stored in glucose is converted into ATP using oxygen through a
series of enzyme-controlled reactions called aerobic respiration.
Glucose + oxygen
carbon dioxide + water + energy
Aerobic respiration occurs in the mitochondria.
More active cells such as brain or sperm cells have more mitochondria to produce
more ATP.
Aerobic respiration has 2 stages;
1. Glycolysis

Glucose is broken down into pyruvate in a process called glycolysis.

Occurs in the cytoplasm & no oxygen is required at this stage.

2 ATP produced per glucose molecule.
2. Aerobic Respiration

Pyruvate from cytoplasm moves into the mitochondria.

Producing water, CO2 and 36 ATP when OXYGEN is present.

In total, during aerobic respiration, 38 ATP is produced.
Aerobic Respiration
Oxygen
Net gain of ATP = 2 + 36 = 38
Fermentation
Location—cytoplasm
Conditions—no oxygen present
2 ATP produced
During fermentation glucose is only partly broken down.
Glycolysis occurs producing pyruvate which is then converted into either lactate/
lactic acid (animal muscle cells) OR ethanol and carbon dioxide (yeast and plants).
Fermentation in Animal muscle cells

Produce lactic acid from pyruvate in process called muscle fatigue.

Reaction is reversible when oxygen debt is repaid.
Fermentation in plant or yeast cells

Produces alcohol (ethanol) and carbon dioxide.

Reaction is irreversible, alcohol builds up killing the organism.
Respiration
Measuring Respiration
Organism takes in oxygen which can be seen by measuring the time taken for the
coloured liquid to be drawn up the tube in a respirometer.
The carbon dioxide exhaled is removed by a carbon dioxide absorbing chemical in test
tube to ensure oxygen is drawn up the tube.
Respiration Summary Table
Aerobic Respiration
Fermentation
38 ATP
2 ATP
Location
Cytoplasm then mitochondria
Cytoplasm
Products
CO2 & water
Net energy
Animal
– lactic acid
Plants
– ethanol & CO2
& yeast