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Topic 4
What is a species?
‘’A group of organisms with similar morphology, physiology and behaviour, which can interbreed to produce
fertile offspring and which are reproductively isolated (place, time or behaviour) from other species
...
It includes:
-

-

Species diversity:the number of different species and
abundance of each species in an area
...


Natural selection increased biodiversity
through adaptation and evolution
...

Conservation helps maintain biodiversity,
especially for endemic species because they’re
vulnerable to extinction
...


Species diversity in a habitat
A habitat is the place where an organism lives and species diversity allows comparison between different habitats
...
Greater species richness = more species in
the area
...


-

Count the number of different species and the individuals of each species
...

A sample of a population is taken and estimates are made based on it
...

2
...

4
...


Choose a random area to sample within the habitat
Count the number of individuals of each species in the sample area
Plant = quadrat
Flying insects = sweep net
Ground insects = pitfall trap
Aquatic animals = net
Repeat the process (more samples)
Use results to estimate the total number of individuals/different species in
the habitat
Must use same sampling technique when comparing different habitats
...
g
...


Genetic diversity
= variety of alleles in a gene pool (the complete set of alleles in a species/population)
Phenotype
-

Observable characteristics of
an organism
Different allelescode forslightly
different versions of the same
characteristics
Larger number of phenotypes =
greater genetic diversity

Genotype
-

Samples of an organisms DNA can be taken so the sequence of base
pairs can be analysed
Order of bases in different alleles is slightly different
Sequencing the DNA shows similarities and differences in the alleles
within a species
Number of different alleles for one characteristic shows genetic
diversity
More alleles = greater genetic diversity

Heterozygosity index (H)
Heterozygotes have two different alleles at a particular
locus (position of a gene on a chromosome)
...

-

An average value for H at many loci can be used to estimate genetic diversity in the whole genome
...


A higher = more diverse area
If all the individuals are of the same species, the index is 1

The index of diversity allows comparison of species diversity
...
There are 11 organisms altogether- 3
red, 5 white and 3 blue
...
44
3(3-1) + 5(5-1) + 3(3-1)
Species occupy different niches
One area can have many different habitats (where an organism lives) which have a set of conditions that support a
distinctive combination of organisms
...
Various populations in a habitat make a community
...
’’
-

Interactions with living organisms (prey/predators)
Interactions with the non-living environment
(oxygen breathed in, carbon dioxide breathed out)

A niche can only be occupied by one species which avoids competition
...

NOTE: some species may look like they’re filling the same niche (e
...
both bats eat insects) but there are slight
differences (e
...
they use different frequencies for their echolocation)
...
g
...
g
...
g
...


antibodies which kill other species
of bacteria in the area, creating less
competition
...


Evolution
1
...

3
...

5
...


Mutations introduce new alleles into a population so
phenotypes vary
...
Fewer individuals mean less competition for
resources
...

Over generations, this leads to evolution as the allele frequencyincreases and the favourable adaptations
become more common
...

A bigger gene pool (more different alleles of each gene) = greater genetic diversity

Speciation:

Seasonal changes

= development of a new species when
populations of the same species become
reproductively isolated
...


-

Individuals from the same population develop different
flowering/mating seasons or become sexually active at
different times of the year
...
g
...

-

Conditions on either side of the barrier will be slightly different e
...
different climate
Natural selection will create different characteristics due to different selection pressures

Different characteristics will be advantageous on each side so the allele frequency will change in each
population
-

Frequency of the advantageous allele will increase on one side of the barrier

Mutations will take place independently in each population, changing the allele frequencies and phenotype
frequencies
...

Eventually the different populations will have become genetically distinct and won’t be able to breed or produce
fertile offspring = reproductively isolated
...

HARDY-WEINBERG EQUATION
Evolution is a change in allele frequency
...

the H-W equation are used to estimate the frequency of particular alleles,
phenotypes and genotypes in a population
...

-

Large population
No immigration,
emigration, mutations or
natural selection
Random mating

If allele frequency does change
then all of these have happened
...


Classification
Taxonomy involves naming and grouping organisms based on similarities/differences in
phenotypes and genotypes, making it easier to identify/study them
...


Genus: shared by
all closely
related species
e
...
Equus- all
horses and zebras

2
...


Three domains:
1
...

3
...

-

Five kingdoms:
1
...

3
...

5
...

Animal ‘finger print’

Multicellular eukaryotes that are autotrophs (organisms that make their
own organic molecule by photosynthesis, except a few parasites)
-

Multicellular eukaryotes that are heterotrophs that absorb
nutrients from decaying matter after external digestion
...

Other organisms with a nucleus are placed in eukaryote
...
New discoveries are shared in meetings and scientific journals and if there’s agreement,
an organism can be reclassified or lead to changes in classification system structure
...


Molecular phylogeny:
-

Study of evolutionary relationships in a group of organisms
Phylogeny tells us which species are related to which and how closely related they are
Looks at DNA and proteins to see how closely related organisms are (more closely related will have
similar molecules)

Phylogenetic trees represent the evolutionary relationships based on the best existing evidence (includes fossils)

Processing new findings
-

Findings are reported in a scientific journal, conference papers or the
internet
...
g
...
Many ignored this idea
but more papers were published by other scientists and there were conferences
held
...

-

Organisms in each of the three domains contain RNA sequencing that is
unique to their domain
...
If the population declines some alleles
may be lost and the genetic diversity decreases
...
E
...
g
...

Genetic diversity can be visible through phenotypes but can also be measured by species richness and species
evenness
...
In species-rich ecosystems, such
as rainforests, habitats will show more even species composition
...
The idea was
adopted as a way of focusing conservation effort on the
most critical places
...

DNA can be cut into fragments and then separated using electrophoresis
...


Heterozygosity index quantifies genetic diversity- calculates the proportion of genes that are present in
heterozygous form
...

PLANT STRUCTURE
All plants…
1
...

3
...


Parenchyma:
-

Tissue found throughout the plant
Cells fill spaces between more specialised tissue
Can have specialised functions

Example:
In roots- role in storage
In leaves- contain chloroplast and form
photosynthetic tissue

Cellulose
-

Polysaccharide made up of beta glucose
units
...

Amylose:

Between 50-80 cellulose chains are linked together
by hydrogen bonds to form microfibrils which
provide structural support
...

Coiled structure making it compact which increases
amount stored in a smaller space
...
The hydrogen bonds are weaker than glycosidic bonds but the large number of hydrogen bonds produces a
strong structure
...

The glue is made of hemicellulose and pectinwhich
both bind to the surface of the cellulose and to each
other to hold the microfibrils together
...

Cellulose microfibrils are arranged in a matrix to
make the cell wall strong and flexible as theyrelaid
down at different angles
...
The cell walls are fully permeable to
water/solutes
...
This aids the movement of substances between cells
...


Tubes for transport and strength
Plants have 3 types of tissue:
1
...

-

Vascular tissue
Involved in transport is surrounded by ground
tissue

3
...

In trees and shrubs the bundles merge to form a continuous
ring as the plant ages
...


-

Tubes found in bundles

-

They’re longer than wide

-

Hollow lumen (no cytoplasm)

-

End walls between cells are perforated

-

Walls thickened and stiffened with lignin, which also waterproofs it

-

Water and ions move in/out of vessels through pits where there’s no lignin

It leaves dead, empty
cells that form a tube
...


Water is transported through TRANSPIRATION

Cohesion- tension theory is that water molecules have cohesive forces as a result of hydrogen bonding
between water molecules
...

Xylem provides a mass flow system for the transport of inorganic ions e
...
nitrate ions are needed to make
amino acids
...


Lack of magnesium = unable to make chlorophyll so older leaves become yellow with brown tints

2
...
Nitrate ions are
required for growth of plant, fruit and seeds
...


Lack of calcium = stunted growth as Ca ions help in the structure of the cell wall and permeability of the
cell membrane

4
...


-

Section of phloem sieve tube between sieve plates is a sieve tube element
which has no nucleus, thin layer of cytoplasm and few organelles
...

The companion cells perform the metabolic processes to maintain the sieve
tube e
...
provide energy for active transport of solutes

Organic molecules are transported through TRANSLOCATION
Sugars and amino acids
are transported in the fluid
in the lumen
...


Solutes are actively transported in and out of phloem


Products of
photosynthesis pass
into the transfer
cell(type of parenchyma
cell)



Transfer cells help to
actively transport
solutes into the sieve
tube



Transfer cells have many
small infoldings to
increasesurface area



Plasmodesmata link the
transfer cell cytoplasm
with that of adjacent
cells



Mitochondria in
transfer cells provides
energy necessary to load
solutes into the sieve
tube



Photosynthetic
products are actively
unloaded from the
phloem into sink
where it will be used


Examples of sinks:
roots, buds, flowers
and developing fruit



Starch can be stored
in roots, bulbs or
tubers in winter
...




Water is polar so
organic molecules can
dissolve in it to be
transported
...
Loading solute into
the phloem increases solute concentration which draws water in by osmosis from adjacent xylem vessels
...

Solutes are unloaded at sinks which lowers solute concentration and so water moves into the xylem by
osmosis, which lowers hydrostatic pressure
...

Xylem and sclerenchyma for support
Phloem sieve tubes, companion cells and transfer cells do not have lignified cells
so don’t provide support
...

-

Sclerenchyma fibres die when lignified, leaving hollow fibres
...
The plant stem relies on tightly packed, fully turgid parenchyma cells
to maintain shape and keep it erect
...

Turgor supports the leaves of all plants
If a cell loses water, turgor is lost
If a high proportion of a plants cells lose their turgidity, the plant wilts
Useful plant fibres

Plant fibres are long, thin, flexible and strong
...

-

-

Mats of fibres are used to absorb heavy metals and hydrocarbons from
polluted water
Plant fibres can be added to other materials to form
biocompositeswhich are renewable, biodegradable and easier/safer
to handle
...
Animals will be deterred
from feeding in the future
...

-

Exponential growth -> in 24 hours E-coli with a generation time of 20 minutes would produce 272 bacteria
(24 hours into minutes, then divide by 20)

Bacteria need optimal conditions where there are:
-

Sufficient nutrients
Optimum temperature
Optimum pH
No build-up of toxic waste products
Sufficient oxygen for aerobic respiration

1
...

3
...


Lag phase- cells adjust to conditions
Log phase- cells divide at the fastest rate
possible for conditions
Stationary phase- growth is limited by lack of
food, build of toxins, changing pH
Death phase- number of cell deaths is greater
than cells formed
...
g
...

Mint produces menthol andcarvone which are toxic to microbes/insects but creates good taste
...
It’s important because
some bacteria are resistant toantibiotics
...

Medicines in plants

Foxglove was used to treat dropsy(oedema)
...
It cured one person, giving them a fuller, more regularheart beat but
then one woman nearly died so he gave up the investigation
...


-

He then tested for correct dosage
...

1
...


Substances are analysed and the active ingredientis identified and copied so it can be manufactured
synthetically
Slight variations of the chemical structure are made in case they have a better effect(can be computer
modelled)

Then…

Clinical trials Phase I

Clinical trials Phase II

-

Tests on animals and isolated cell/tissue
Assess safety and effectiveness
Can take years
Authorised by independent scientists, doctors and members of the public to
avoid any bias

-

Pre-clinical testing

Small group of healthy volunteers are given different doses
Tests confirm whether the compound is used by the body in the way predicted
by laboratory tests
Tests for safety

-

100-300 patients with the disease are treated to test effectiveness

Clinical trials Phase III

Double-blind randomised controlled trial
-

Afterlicensing

-

Large group (1000-3000) is divided into 2 groups
One group is given the compound, other group given the placebo or an existing
standardised treatment
Tests for side effects and effectiveness
Can be licensed and sold
Trials continue to collect data on the effectiveness/safety of a new drug after
this one has been licensed
...
The outer layers of the seed
become lignified to form the seed coat which protects the embryo
...


Endosperm:
-

Stored food on the outside of the embryo
Common in monocotyledons (one leaf)
Creates endospermic seeds

Dispersal helps offspring to avoid competing with parent
plants/each other and helps to colonise new habitats
...


In many dicotyledons (two leaves) the embryo absorbs nutrients from the endosperm and stores it in the seed
leaves (cotyledons) which swell to fill the seed
...

When conditions are suitable and dormancy has been broken, the seed takes in water through a small pore in the
seed coat
...

Gelatinisation:

-

When starch granules are heated in water they suddenly swell¸
absorb the water and thicken the liquid
...
Starch mixture
applied to the surface is gelatinised and then cooled so it forms bonds between the starch molecules, stiffening the
fabric
...

Super- absorbents
If starch is chemically cross linkedbefore it is gelatinised, particles are formed that can be dried
...

Starch foam
Amount of water present determines the temperature at which the starch
gelatinises
...
g
...
As hot
starch leaves through a small
exit hole, pressure is released
and so it expands are the
water turns into steam
...
Plant based
plastics have been developed that are made by fermentation of sugars which means that supermarket food
packaging can be made from starch- bioplastics
...
Fuel made from starch e
...
bioethanol or
biodiesel
...

Oil reserves will run out
Plastics generate non-biodegradable waste, which creates waste
disposal problems

Fossil fuels release carbon stores built up over long periods of time
...

The demand for food won’t
change so land needs to be
available to grow crops
...
If buried deep in a landfill site
it will not be able to decompose due to lack of oxygen
...


-

Many uncultivated areas are unsuitable for agriculture or are needed for something elsee
...
wildlife
conservation/water conservation

-

Intensive agriculture is very energy demanding (ploughing, harvesting, fertilising)

-

Human population is increasing rapidly

-

Some plant alternatives do not have the same desirable qualities as the oil-based products

-

Some plant alternatives may require higher energy consumption
during production and transport
THE ROLES OF ZOOS

Zoos help to protect and manage endangered species because of a low
population or a threatened habitat
...


Scientific research

2
...

How is genetic variation lost?
Genetic drift
In a small population, some of the alleles are not
passed on by chance
...

Inbreeding depression
In a small population, the likelihood of closely
related individuals mating increases
...

-

Individuals inherit recessive alleles from both parents
Homozygous recessive genotype accumulates
Many recessive alleles have harmful effects so results in inbreeding depression

Offspring are less fit(less able to survive and reproduce)- may be smaller, females produce less eggs and have a
shorter life
...

Ensures that genes are equally represented
in the subsequent generations
...

Some studbook records are supported by
techniques of cytogenetics(structure of
chromosomes)
and
of
molecular

biology(studying nature of genes)
...

3
...

Animals need to learn the skills needed for survival in the wild

Educational school trips to the zoo
are often arranged
...
If it becomes extinct then a
new plant can be grown
...
g
...

A month later a sample is taken out and germinated on agar plates to test for viability
Once the plant grows, seeds are harvested again
The plants are checked every 10 years

Some tests can be carried out as school projects, supported by the Royal Botanic Gardens
...




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