biology unit 2 notes
TRANSCRIPT
Biology Unit 2 Notes
Topic 3: the voice of the genome
Cells and Organelles
Prokaryotic cells
o Small and simple cells.
o No nucleus and no membrane bound organelles.
o DNA is circular and free floating in the cytoplasm
o Always have a cell wall
o Contain plasmids (rings of DNA) and a flagellum
(used for movement to propel the cell)
o Include bacteria cells like E-coli.
Eukaryotic cells
o Complex cells, which include animal and plant cells.
Organelles:
Nucleus:
o Surrounded by a nuclear envelope
(double membrane), which contains
pores.
o Contains chromatin – genetic
material which controls the cells
activities
o Pores allow substances like RNA to
move between the nucleus and
cytoplasm
o The nucleolus makes RNA and
ribosomes.
Ribosomes:
o The site where proteins are made
o Consist of small and large subunits.
o Very small organelle that is either attached to rough endoplasmic reticulum or floats free in
cytoplasm
Mitochonadria:
o Has a double membrane
o It is the site of respiration where ATP is produced
o Inner membrane is folded to form structures called cristae
o Matrix contains enzymes involved in respiration
o Found in large numbers in cells that are active and require a lot of energy
Golgi apparatus:
o Group of flattened sacs
o Vesicles often seen at the edges
o The golgi processes and packages substances made by the cell, mainly lipids and proteins
o Also makes lysosomes
Lysosomes:
o Round organelle surrounded by a membrane
o Contains digestive enzymes that are kept separate from cytoplasm
o Can be used to digest invading cells or to break down worn out components of the cell.
o They can completely break down cells after they have died (Autolysis)
Rough Endoplasmic Reticulum (RER)
o System of membranes enclosing a fluid filled space
o Continuous with the membrane of nucleus
o Surface is covered with ribosomes
o Transports proteins which have been made in ribosomes
Smooth Endoplamic Reticulum:
o Similar to RER but no ribosomes
o Transports lipids around the cell
Centrioles:
o Every animal cell has one pair of centrioles
o They lie at right angles to each other, and close to the nucleus
o Under a microscope: appear as nine bundles of tiny microtubules arranged in a
circle
o Involved in the formation of the spindle fibres in cell division – spindle fibres are
microtubules.
Microtubules:
o Hollow cylinders, found throughout the cytoplasm
o Made from a protein called tubulin.
o Help other organelles to move from place to place in the cell
The roles of the Rough Endoplasmic Reticulum, Golgi apparatus and vesicles in protein transport:
1. Proteins made on ribosomes on the RER
2. Proteins enter the RER cisternae (space inside lamellae)
3. Vesicles containing the protein are budded off the RER
4. Vesicles move along microtubules to the Golgi and
are added on
5. Protein is chemically modified, processed and
‘finished off’
6. Vesicles are budded off the Golgi and move to the
cell surface membrane, along microtubules
7. Vesicles fuse with the membrane and the contents
are releases. This is called secretion or exocytosis.
Cell organisation:
Multicellular organisms like humans are made of many different types of cells. Cells need to be
organised into groups to work together.
Similar cells organised into tissues: - one or more similar cells are organised together, and carry out
a particular function. E.g.: Four main tissue types in the human body: epithelial, connective, nervous
and muscle tissue.
Tissues are organised into organs: - group of different tissues working together to perform a
particular function: E.g.: the lungs are made up of: squamous epithelium tissue, fibrous connective
tissue and blood vessels.
Organs are organised into systems: - Each system has a particular function. E.g: digestive system
includes the organs: stomach, pancreas, small and large intestines.
The cell cycle and Mitosis:
Mitosis:
o Cell division to produce new cells for growth, repair of damaged tissues and asexual
reproduction.
o Mitosis produces two ‘daughter’ cells from one parent cell, and the two cells have the same
number of chromosomes and are genetically identical to each other and to parent.
The Cell Cycle:
Interphase (G1, S, G2):
o G1: gap phase. Period of cell growth and new organelles and
proteins are made.
o S phase: Synthesis of DNA – replicated.
o G2: gap phase. Period after DNA duplication and cell prepares
for division.
Mitosis:
Prophase:
o Chromatin condenses, getting shorter
and fatter, and form chromosomes with
each chromosome having two
chromatids joined by a centromere.
o The nucleolus breaks down
o Centrioles start moving to opposite
poles of the cell and begin to form the
spindle fibres across it.
Metaphase :
o The spindles made of microtubules
have been fully formed by the
centrioles.
o The chromosomes align along the
middle of the cell, and become
attached to the spindle by their
centromeres.
Anaphase:
o The centromeres divide, separating the paired chromosomes (sister chromatids).
o The chromatids begin to move towards opposite poles
Telophase:
o Chromatids reach the opposite poles on the spindle, and are now known as
chromosomes.
o Nuclear envelope forms around each group of chromosomes
Cytokinesis:
o Cytoplasm splits, and there are now two distinct daughter cells
Core practical – observing mitosis
Preparing and staining a root tip to observe the stages of mitosis:
1. Cut 5mm of the tip from a growing root (e.g. garlic)
2. Place root tip on a watch glass (small shallow bowl) and add one drop of
hydrochloric acid – helps to soften and break down the membranes and helps stain
to be absorbed easily by the chromosomes
3. Add 10 drops of stain (e.g. acetic orcein) so that the chromosomes darken and can
be seen under microscope – ratio of stain to hydrochloric acid should be 10:1
4. Warm the watch glass on a hotplate for 5 minutes
5. Place the root tip on a microscope slide and use a needle to break it open and
spread the cells out thinly
6. Add a few more drops of acid
7. Cover with cover slip, and squash it down gently (you can warm the slide again for a
few seconds to intensify the stain)
8. Observe under microscope
Meiosis and the production of gametes
o Sexual reproduction is the production of a new individual resulting from the joining
of two gametes
o Each organism must inherit a single copy of every gene from each of its “parents.”
o Gametes are formed by a process that separates the two sets of genes so that each
gamete ends up with just one set – n=23 chromosomes.
Meiosis: - cell division to produce haploid gametes
o Process of reduction division in which the number of chromosomes per cell is cut in half
through the separation of homologous chromosomes in a diploid cell.
o Involves two divisions, meiosis I and meiosis II.
1. DNA replicates, so there are two identical copies of each chromosome
2. DNA condenses to form chromosomes made of two sister chromatids
3. The chromosomes arrange into homologous pairs – pairs of matching chromosomes
4. The first division happens- homologous pairs are separated and chromosome number is
halved
5. Meiosis 2 - Second division (similar to mitosis) – pairs of sister chromatids are separated
6. Four new cells (gametes) are produced that are genetically different
How does meiosis produce genetically different gametes?
Crossing over of chromatids:
o During meiosis 1, homologous pairs of chromosomes come together and pair up.
o Two of the chromatids in each homologous pair twist around each other and exchange
portions of their chromatids.
o Crossing over produces new combinations of
alleles
o This increases the genetic variation
Independent assortment of chromosomes:
o Happens during meiosis 1
o The homologous pairs line up randomly
o Maternal and paternal chromosomes from parents are therefore randomly distributed into
gametes.
Mammalian gametes
Sperm:
o Flagellum/tail: allows sperm to swim to egg cell
o Acrosome contains hydrolytic/digestive enzymes to break down the egg
cell’s Zona Pellucida and penetrate the egg
o Contains lots of mitochondria to provide energy for swimming
Egg cell:
o Surrounded by follicle cells which form a protective layer
o Jelly like protective layer between the cell membrane and follicle cells
called the Zona Pellucida, which sperm must penetrate
Fertilisation:
o Moment when nuclei of male and female gametes fuse
o Creates cell with full number of chromosomes – the zygote
Mammals:
Fertilisation occurs in the oviduct:
1. Sperm swim toward egg cell in oviduct
2. Once sperm contacts the zona pellucida (Z.P) of the egg cell, the acrosome reaction
occurs. This is when the digestive enzymes are released from the acrosome, and digest
the Z.P so that the sperm can move towards the cell membrane of egg.
3. The sperm head fuses with the cell membrane of the egg. This triggers the cortical
reaction, where the egg cell releases the contents of vesicles called cortical granules into
the space between the cell membrane and Z.P
4. This alters the Z.P and prevents other sperm from reaching and fertilising the egg.
5. The sperm nucleus enters the egg cell, and the tail is discarded
6. Nucleus of sperm fuses with nucleus of egg – fertilisation
Fertilisation in plants:
1. Male gamete: Pollen grain, female gamete: inside ovule of ovary
2. Pollen grain lands on stigma of flower, and begins to germinate (The pollen grain
must be from the same species)
3. A pollen tube grows out of the pollen grain and moves down the style
4. There are three nuclei in the pollen tube – two male gamete nuclei and one tube
nucleus at the tubes tip. The tube nucleus makes enzymes that digest surrounding
cells to make way for the pollen tube.
5. When the pollen tube reaches the ovary, it passes through the micropyle of the
ovule (small hole), and then into the embryo sac
6. The tube nucleus disintegrates, and the tip of the pollen tube bursts and the two
male nuclei are released
7. One male nucleus fuses with will the egg nucleus to form a diploid zygote. The other
male nucleus fuses with the two polar nuclei, to form the endosperm, which is
triploid (3n), and it is a food store for the mature seed
8. This is known as a double fertilisation
Cell differentiation:
o Stem cells are unspecialised cells that can develop into many different types of cells.
o All cells in the body are derived from stem cells. The process of cell specialisation is called
differentiation.
o There are two main types of stem cells: embryonic and adult stem cells.
o Potency refers to the differentiation potential (the potential to differentiate into different
cell types) of the stem cell. The three types are:
1. Totipotency: The ability of a stem cell to produce all cell types, this includes all
specialised cells in an organism and extra-embryonic cells (cells of the umbilical cord
and placenta). Their potential is ‘Total’. A fertilised egg is totipotent.
2. Pluripotency: The ability to produce all the specialised cells in an organism, but NOT
extra-embryonic cells.
3. Multipotency: The ability to produce a number of different cells, but is limited in its
differentiating ability
Embryonic stem cells:
o Obtained from early embryos.
o To do this in a laboratory, IVF (In-vitro fertilisation) is carried out. Once the human egg has
been fertilised, it will develop into a blastocyst which consists of cells called the inner cell
mass. These cells are then transferred to a culture medium where they are cultured into
embryonic stem (ES) cells. ES cells are pluripotent- they can differentiate into almost any
type of cell in the human body.
Adult/somatic stem cells:
o Found in body tissues of an adult, e.g. can be found in bone marrow.
o They can be extracted and obtained by an operation with very little risk involved.
o The donor is anaesthetised and a needle is inserted into the centre of the bone, usually
from the hip, and a small amount of bone marrow is removed. This operation can cause
a lot of discomfort to the person.
o However, adult stem cells are multipotent and can only differentiate and produce a
limited number of cell types.
Stem cells in medicine:
o Stem cells can potentially be used to replace damage tissues in a range of diseases.
o Scientists are researching the use of stem cells for treatments for conditions such as:
o Spinal cord injuries: stem cells can be used to repair damaged nerve tissue
o Parkinson’s sufferers: stem cells to replace the lost or faulty nerve cells that produce
dopamine.
Arguments for the use of stem cells:
o Can save many lives
o Can improve the quality of life for many people e.g. replacing damaged cells in the eyes of
people who are blind.
Arguments against the use of stem cells:
o Obtaining stem cells from embryos by IVF raises ethical issues – viable embryos are
destructed and could have been a potential human life.
o Many people believe that life begins at conception, and it is immoral and wrong to destroy
and embryo, even to reduce suffering in existing human life.
o Scientists are ‘playing god’ and ‘messing with human life’
Society has to consider all the arguments for and against stem cell research before allowing it to go
ahead. To help society make these decisions, regulatory authorities have been established, such as
the Human Fertilisation and Embryology Authority (HFEA)
The work of regulatory authorities includes:
o Looking at proposals of research – this ensures that research involving embryos is carried
out for a good reason, and is not repeated elsewhere
o Licensing and monitoring centres involved in embryonic stem cell research – ensures that
only fully trained staff carry out the research, and helps to avoid unregulated research.
o Producing guidelines and codes of practice – ensures that scientists use similar methods for
comparison of results, and ensures that methods of extraction are controlled.
o Monitoring developments and advancements in research – ensures that all the guidelines
are up to date with the latest scientific understanding
o Providing information and advice to governments and professionals – helps society to
understand what’s involved and why it’s important.
Core practical: demonstrating totipotency by using plant tissue culture:
o Plants have stem cells that can be found in the roots or shoots.
o All stem cells in a plant are totipotent – can grow into a whole new plant.
1. Sprinkle seeds of white mustard onto a damp sponge in a plastic tray, cover with transparent
cling film and place in warm light place to germinate. When seedlings have started to unfold
cotyledons (seed leaves) they are ready to culture
2. Cut seedlings just below the growing tip
3. Push the cut end of the plant in a growth medium, e.g. 2cm depth agar in a McCartney
bottle (agar contains nutrients and growth hormones) Make sure the cotyledons don’t touch
the agar
4. If conditions are suitable (e.g. right hormones) unspecialised cells will grow into specialised
cells.
5. Eventually the cells will grown and differentiate into an entire plant.
Cell specialisation through differential gene expression:
o Stem cells become specialised because different genes in their DNA become active (or
turned on)
o Under the right conditions, some genes are activated and other genes are inactivated
o mRNA is only transcribed from the active genes
o This is then translated into proteins
o The proteins modify the cell – they determine the cell structure and control cell
processes (including activation of more genes, which produces more proteins)
o Changes to the cell produced by these proteins cause the cell to differentiate and
become specialised.
o EXAMPLE: Red blood cells are produced from stem cells in the bone marrow, which
contain a lot of haemoglobin and have no nucleus. The stem cell produces a new cell on
which the genes for haemoglobin production are activated, and other genes such as
those involved in removing the nucleus are activated too. Many other genes are
activated or inactivated resulting in a specialised red blood cell.
Variation
Variation in phenotype: can be continuous or
discontinuous.
E.g.: height, mass and skin colour are all examples
of continuous variation because there is a range,
and no distinct categories, whereas blood group,
and sex (male or female) show discontinuous
variation because there are distinct categories that
an individual can fall into.
Variation in phenotype is influence by variation in genotype:
o Individuals of same species have different genotypes (combinations of alleles)
o Variation in genotype(genes) results in variation in phenotype (physical characteristics)
o Some characteristics are controlled by only one gene – monogenic. They tend to show
discontinuous variation, e.g. blood group.
o Most characteristics are controlled by a number of genes, at different loci – polygenic.
They tend to show continuous variation, e.g. height
Interactions between genes and the environment
Expression of phenotype is a result of interaction between genes and environment. Siamese cats
have dark coloured fur on their extremities. This is caused by an allele that controls pigment
production that only functions at the lower temperatures of those extremities. Environment
determines the phenotypic pattern of expression.
Some characteristics are only influenced by genotype e.g. blood group. Most characteristics are
influenced by both genotype and the environment e.g. weight
o Height –polygenic and affected by environmental factors, esp. Nutrition.
o Monoamine Oxidase A (MAOA) – enzyme that breaks down monoamines, which are
chemicals in humans. Levels of MAOA are genetically determined by a single gene
(monogenic), but smoking tobacco and anti-depressants can reduce the amount
produced which can lead to mental health problems as well as diseases such as
Parkinson’s.
o Cancer is the uncontrolled division of cells that leads to tumours. The risk of cancer
development is affected by genes, but many environmental factors such as diet and
smoking can also influence the risk
o Animal hair colour is polygenic and the environment also plays a part in some animal.
E.g. temperature can trigger changes in fur colour.
Topic 4: Biodiversity and natural resources
Plant structure
Animal cell Plant Cell
Cell surface membrane only – no cell wall Cellulose cell wall surrounds the cell
Contains lysosomes and centrioles Does not contain lysosomes or centrioles
Glycogen granules used for storage Starch grains used for storage
No chloroplasts Chloroplasts present
Sometimes vacuole present and they are small and scattered
Large vacuole filled with sap
Ultra structure of plant cells:
o Plasmodesmata
Channels in the cell walls that link adjacent
cells together – allow the transport of
substances and communication between cells
o Pits
Regions where cell wall is thin. Arranged in pairs, and allow for the transport of substances
between cells
o Chloroplasts
Small, flattened structure surrounded by a double
membrane and is the site of photosynthesis.
Grana – stacked up thylakoid
Stroma – matrix which contains enzymes needed for
photosynthesis
o Amyloplasts
Contains starch granules, and can convert it to glucose to release when plant requires it for
respiration
o Vacuole and tonoplast
Vacuole contains cell sap – made up of water, enzymes, minerals and waste products.
Keeps the cell turgid – stores water and prevents plant from wilting
The tonoplast is the membrane that surrounds the vacuole – controls what enters and
leaves it.
Cellulose and starch
o Starch: the main energy storage material in plants.
1. Mixture of two polysaccharides of alpha glucose – amylose and amylopectin
o Amylose: long, unbranched chain of alpha glucose. Has a coiled structure, which
makes it compact and good for storage
o Amylopectin: long, branched chain
o of alpha glucose. The side branches allow for the enzymes to break it down quickly.
2. Starch is insoluble in water – good for storage
o Cellulose: the major component of cell walls in plants
1. Long unbranched chains of beta glucose joined by glycosidic bonds
2. Straight chains.
3. Between 50 and 80 cellulose chains are joined together by many hydrogen bonds to
form strong threads – microfibrils.
4. The strong threads provide structural support.
Plant cell wall:
o Made up of largely insoluble cellulose
o Gives plant its strength and support
o When the beta glucose join together, every other monomer unit is inverted so bonding can
take place
o The linking of b-glucose molecules means that the hydroxyl groups stick out on both sides of the molecule. This means hydrogen bonds can form between the partially positively charged hydrogen atoms of the hydroxyl groups and the partially negatively charged oxygen atoms elsewhere in the molecule.
o This is known as cross-linking and holds neighboring chains firmly together. o Between 50 and 80 cellulose chains are linked together by hydrogen bonds to form strong
threads - microfibrils.
o Cellulose microfibrils are laid down in layers held together by a matrix of hemicelluloses and
other short chain carbohydrates which act as a kind of glue
The plant wall consists of several layers:
Middle lamella:
o The is the outermost layer of the cell
o It is shared between two adjacent plant cells
o Made mostly of the polysaccharide pectin, and acts as an adhesive sticking together
adjacent plant cells
o Gives plant stability
Primary cell wall:
o Next to middle lamella
o Made up of randomly arranged cellulose microfibrils embedded in pectin and hemicellulose.
Secondary cell wall:
o Innermost layer – formed in some plants after the primary cell wall has fully grown
o Made up of neatly arranged cellulose microfibrils – run parallel to each other
o Lignin (woody like substance) is often deposited in the secondary cell wall – lignification. This
gives the plant extra tensile strength (only happens in some plants such as trees which are
made up of wood) – makes it impermeable
o The microfibrils are held in pectin, hemicelluloses and sometimes lignin.
Primary cell wall Secondary cell wall
Plant stems: Sclerenchyma cells and xylem vessels:
Xylem vessels:
o Found throughout the plant, particularly
around centre of the stem
o Provides a passage for transportation of
water and dissolved mineral ions from the
root system to the leaves.
o Made of long, tube like structures formed
from dead cells, joined end to end.
o Found together in bundles.
o Have a hollow lumen (no cytoplasm) and
have no end walls – uninterrupted tube
o Walls are thickened with lignin which helps to support and strengthen the plant.
o Water and mineral ions move into and out of the vessels through pits in the walls
where there is no lignin
Sclerenchyma fibres:
o Provide support
o Made of bundles of dead cells, and also have hollow lumen and no end walls
o Have strong secondary walls which are thickened with lignin
o They develop as the plant gets older to support the increasing weight of the plant
Uses of plant fibres and how they may contribute to sustainability:
o Plant fibres are made of long tubes of plant cells e.g. sclerenchyma cells and xylem tissue
that are very strong.
o 2 reasons:
1. The cell wall contains cellulose microfibrils in a net-like arrangement – this gives the
plant fibres a lot of strength
2. Secondary thickening of cell walls is when a secondary cell wall grows. It’s a much
thicker layer than the primary cell wall, and the cellulose microfibrils and extra lignin
make it very strong and rigid
o Plant fibres can be used to make ropes or fabrics like hemp.
o Making products from plant fibres is more sustainable than making them from oil. This is
because crops can be re-grown to maintain the supply for future generations, and less fossil
fuel will be used up.
o Products from plant fibres are also biodegradable, unlike most oil based plastics.
o Plants are easier to grow and extracting the plant fibres is easy compared to extracting and
processing oil. E.g. natural decomposers can be used to break down the material around the
fibres – this is known as retting.
Starch:
o Found in all plants
o Some plastics can be made from plant-based materials like starch – called bioplastics
o Fuel can also be made from starch. E.g. bioethanol.
o This is more sustainable – again, because crops can be re-grown and less fossil fuel is
used up.
Core practical – measuring the tensile strength of plant fibres
o Tensile strength – maximum load the fibre can take before it breaks.
1. Plant material - stinging nettles- should be left to soak in a bucket for a week to
make fibre extraction easier (retting). Or, celery can be used and should be left in
beaker of coloured water for fibres to be seen easily and pulled out.
2. Once fibres removed, measure lengths of fibres used (must all be the same length)
and then connect between two clamp stands
3. Gradually add mass in the middle until the fibre breaks, and record the mass.
4. Repeat the experiment with different samples of the same fibre – to increase
reliability.
5. Must make sure other variables are constant – temperature, size of each individual
mass used.
Safety precautions: wear goggles to protect eyes and make sure the area where
weights will fall is clear.
Importance of water and inorganic ions to plants
o Water is needed for photosynthesis, to maintain structural rigidity, transport minerals and
regulate temperature.
o Magnesium ions – Needed for the production of chlorophyll. Deficiency results in yellow
areas developing and growth slows down
o Nitrate ions – Needed for production of DNA, proteins and chlorophyll. Deficiency results in
stunted growth, poor seed and fruit production and leaves appear light green/yellow.
o Calcium ions – Important components of plant cell wall, and required for plant growth.
Deficiency results in leaves turning yellow and crinkly, and poor fruit development.
Core practical: Investigating plant mineral deficiencies
Using Mexican hat plantlets making sure they are the same height.
1. 9 test tubes – 9 different nutrient solutions. 2 used as a control: all nutrients present and
lacking all nutrients
2. Cover test tubes with black paper – this prevents algae growing in test tubes which will take
up the nutrients.
3. Put the nutrient solutions into the test tubes and label each one. Solutions should be filled
to the top so that the roots will be completely submerged. Label each one.
4. Cover test tubes with foil so that solutions don’t evaporate and to keep the plant stable
5. Pierce hole in the top of each one, and gently push the Mexican hat plantlets through the
holes so that it is in the solution below.
6. Put in test tube racks and on a windowsill so that leaves are exposed to sunlight and to
maximise photosynthesis.
7. Check and observe after one week to see effect of the nutrient deficiencies.
Drug testing and drugs from plants
William Withering and his digitalis soup:
o He was a scientist in the 1700s
o Discovered that an extract of foxglove plants could be used to treat dropsy (swelling
brought about by heart failure. The extract contained the drug Digitalis
o Withering made a chance observation, gave digitalis to patients and they were cured, but
some died due to the poisonous nature of foxgloves.
o As a result of this, he tested different versions of the remedy with different concentrations
of digitalis
o Found that dried, powdered form was the most effective.
o Through trial and error he discovered the right amount to give to the patient.
Modern drug testing protocols are more rigorous and controlled:
Must pass each stage of testing to go onto the next:
1. Computers are used to model the potential effects of a substance
2. Tested on human tissues in a lab
3. Tested on animals – this sees the affects it has on an entire organism. Testes on rats and
mice and then rodents and non-rodents to compare to other animals.
4. CLINICAL TRIALS – three phases
Phase 1: Drug tested on small group of healthy volunteers – to find out whether its a
safe dosage and to see how the body reacts to the drug.
Phase 2: Drug tested on a larger group of patients with the disease – to see how well
the drug actually works
Phase 3: The drug is compared to existing treatments – hundreds or thousands of
patients. They are randomly split into two groups, one receives new treatment, and
other group receives existing treatment. This aims to see if the new drug is better than
existing drugs.
During phase 2, the patients are split into 2 groups, and one is assigned a placebo – this allows
scientists to see if the drug actually works compared to a placebo.
Phase 2 and 3 – double blind study design – the doctors and patients don’t know who has been
given the placebo or the drug, or in phase three the existing or new treatments. This reduces bias.
Core practical - investigating antimicrobial properties of plants
Equipment: agar plate seeded with bacteria, plant material: e.g. garlic and mint, pestle and mortar,
10cm^3 industrial denatured alcohol, sterile pipette, paper discs, sterile Petri dish, sterile forceps,
hazard tape, marker pen
1. Make plant extracts by crushing 3g of plant material with 10cm^3 alcohol and shake
occasionally for 10mins (must shake for long time to ensure there is enough active
ingredient)
2. Pipette 0.1cm^3 of the separate extracts onto sterile paper discs, and place on the sterile
Petri dish and allow it to dry. Two paper discs are controls: With water and with nothing.
3. Label the agar plates with the different plant extracts and split into 4 sections, 1 for each
type of extract.
4. Place the discs into each quadrant of the agar plate and close and tape with hazard tape.
5. Leave to incubate and observe zone of inhibitions.
Outcome: control discs completely covered with bacteria, and some plant extracts will have larger
inhibition zones than others which show they are more effective at lower concentration.
Must make sure surfaces, and all equipment used is STERILE, otherwise unwanted microbes will
grow on the agar plates.
Adaptation and evolution:
Niche – the role of an organism or species within its habitat, its way of life. Includes its interactions
with other living and non-living environment.
o Every species has its own unique niche, and a niche can only be occupied by one species.
o If two species try to occupy same niche – they will compete and then only one species will
be left.
Adaptations to niche:
Adaptations: features that increase an organisms chance of survival and reproduction
1. Anatomical: structural features of an organisms body/ body characteristics
e.g.: whales and seals have blubber which protects them and has many functions.
2. Physiological: processes inside an organisms body that increases its chance of survival
e.g.: the mammalian diving reflex – allows diving mammals to stay under water for longer
because their heart rate drops and the blood pumps less oxygen.
3. Behavioural: ways an organism acts
e.g.: penguins huddle together to stay warm, and birds of paradise have a special dance
when they want to mate.
Adaptations become more common by evolution:
Natural selection: one of the processes by which evolution occurs. It explains why living organisms
change over time to have the anatomy, functions and behaviour that they have
1. Individuals within a population show variation in their phenotypes and genotypes.
2. Predation, disease, and competition create a struggle for survival
3. Individuals that are better adapted – have characteristics which are favourable and give
them an advantage and are more likely to survive, reproduce and pass on their
advantageous adaptations to offspring.
4. Over time, the number of individuals with the advantageous adaptations increases
5. Over generations, this leads to evolution as the favourable adaptations become more
common in the population.
Biodiversity and Endemism
Biodiversity: the variety of organisms in an area. This includes:
o Species diversity: number of different species and abundance of each species in an area
o Genetic diversity: Variation of alleles within a species or population of species.
Conservation – needed to help maintain biodiversity
Endemism – species unique to a single place. Conservation of endemic species is very important as
they are the most vulnerable to extinction.
Measuring Species diversity:
1. Count number of different species in an area – species richness. The higher the number of
different species, the greater the species richness. However, this gives no indication of the
abundance of each individual species.
2. Count the number of different species AND the number of individuals in each species. Then
use a biodiversity index e.g. Simpson’s Index of Diversity to calculate the species diversity.
This way takes into account abundance of each species.
Samples can be taken to make estimates on whole habitat based on the sample.
1. Choose a random area within habitat to sample – random reduces bias in results.
2. Sampling techniques:
o Plants – use a quadrat (a frame placed on ground)
o Flying insects – sweepnet
o Ground insects – pitfall trap
o Aquatic animals – net
o Then count the number of species in the sample that you’ve got.
3. Repeat, and take as many samples as possible, as it will give a better indication of the whole
habitat.
4. Use results to estimate total number of individuals or total number of different species
(species richness)
5. When sampling different habitats and comparing, the same sampling technique should be
used.
Measuring Genetic Diversity:
o Individuals of the same species are different because they have different alleles
o Genetic diversity is the variety of alleles in the gene pool of a species (or population). Gene
pools are the complete set of alleles in a species or population
o The greater the variety of alleles, the greater the genetic diversity.
o You can measure genetic diversity by looking at:
Phenotypes – observable characteristic of an organism:
o Because different alleles code for slightly different versions of the same characteristics, by
looking at the different phenotypes in a population of a species, you can get an idea of the
diversity of alleles.
o The larger the number of different observable phenotypes, the greater the genetic diversity
Genotype:
o Analyzing an organism’s DNA.
o Different alleles have different orders of base pairs in DNA
o You can measure the number of different alleles a species has for one characteristic to see
how genetically diverse the species is. The larger the number of different alleles the greater
the genetic diversity.
Conservation of biodiversity:
o If a species becomes extinct, or there is a loss in genetic diversity, this causes an overall
reduction in global biodiversity
o There are many endangered species in the world at risk of extinction because of a low
population or a threatened habitat.
o Conservation involves the protection and management of endangered species
o Zoos and seedbanks help to conserve endangered species and genetic diversity.
Seedbanks:
o Store of lots of seeds from many different species of plants
o Conserve biodiversity by storing seeds of endangered plants
o If the plants become extinct in the wild, the seeds can be used to grow new plants
o They also help to conserve genetic diversity. For some plants they store a range of seeds
from plants with different characteristics, hence different alleles. E.g. for tall and short
sunflowers.
o The seeds must be stored in cool, dry conditions – in order for them to be stored for a long
time
o The seeds must be tested for viability (ability to grow into a plant). The seeds are planted,
grown, and new seeds are harvested and returned to storage.
Advantages:
o Cheaper to store seeds than fully grown plants
o More seeds can be stored than grown plants, because they take up less space
o Less labour is required to look after seeds than plants
o Can be stored anywhere, as long as it is cool and dry, whereas plants would need conditions
for their original habitat
o Seeds are less likely to be damaged by disease, natural disaster, or vandalism
Disadvantages:
o Testing for viability can be expensive and time consuming
o Can be difficult to collect seeds
o Expensive to store all seeds and regularly test for viability.
Zoos:
Have captive breeding programmes to help endangered species:
1. Involves breeding animals in controlled environments
2. Endangered or extinct species in the wild can be bred together in zoos to help increase their
numbers e.g. pandas are bred in captivity because in the wild their numbers are very low.
3. However, some animals can have problems breeding outside their natural habitat, which
can be hard to recreate in a zoo. Many people also think it is cruel to keep animals in
captivity even if it is done to prevent extinction.
Reintroduction of plants and animals to the wild:
o Can contribute to restoring habitats that have been lost, e.g. due to deforestation
o However, reintroducing organisms can bring new diseases to habitats, and reintroduced
animals may not behave as they would if they were raised in the wild – e.g. problems finding
food or communicating with wild members of their species.
Education and scientific research:
o Educating people about endangered species and reduced biodiversity raises public
awareness and interest in conservation of biodiversity.
o Zoos allow people to get close to organisms
o Seedbanks provide training and set up local seedbanks all around the world e.g. the
millennium seed bank project aims to conserve seeds in their original country.
o Scientists can study how plant species can be successfully grown from seeds, which is useful
for reintroducing them to the wild.
o Research in zoos increases knowledge about the behaviour, physiology and nutritional needs
of animals which can contribute to conservation efforts in the wild.
o Zoos can carry out research that may not be possible in the wild e.g. nutritional and
reproductive studies
o However animals in captivity may act differently to those in the wild.