Epic Bio Notes (For A-level)

7/30/2019 Epic Bio Notes (For A-level)

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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.


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o Very small organelle that is either attached to rough endoplasmic

reticulum or floats free in cytoplasm

Mitochondria:

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


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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 offthe 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 released. This iscalled 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 thehuman body: epithelial, connective, nervous and muscle tissue.


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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 largeintestines.

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 geneticallyidentical 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:


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Prophase:

o Chromatin condenses, getting

shorter and fatter, and formchromosomes 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 nowknown 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)


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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 chromosomesdarken 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 ofreduction 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


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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 cells Zona Pellucida and penetrate the egg

o Contains lots ofmitochondria to provide energy for

swimming

Egg cell:


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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


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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:


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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 anorganism, 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 whichconsists 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.


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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 Parkinsons 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, regulatoryauthorities 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

ofextraction 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 whats involved and why its important.


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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 dont 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


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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 distinctcategories, 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

Parkinsons.


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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 partin 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 cellwall

Cellulose cell wall surrounds the cell

Contains lysosomes and centrioles Does not contain lysosomes orcentrioles

Glycogen granules used for storage Starch grains used for storageNo chloroplasts Chloroplasts presentSometimes vacuole present and theyare 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


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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 ofalpha 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 breakit 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 ofbeta glucose joined by glycosidic

bonds

2. Straight chains.


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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 thebeta 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 bondscan form between the partially positively charged hydrogen atoms of thehydroxyl groups and the partially negatively charged oxygen atomselsewhere 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

ofglue

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:


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o Next to middle lamella

o Made up ofrandomly 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 ofneatly 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.

Plant

stems: Sclerenchyma cells and xylem vessels:

Xylem vessels:

o Found throughout the plant,

particularly around centre of thestem

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.

Primary cell

wall

Secondary cell

wall


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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. Its 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.


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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 recordthe 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


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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 dont 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 offoxglove 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 theywere cured, but some died due to the poisonous nature of foxgloves.


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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 thepatient.

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 compareto other animals.

4. CLINICAL TRIALS three phases

Phase 1: Drug tested on small group ofhealthy 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 ofpatients 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 dont

know who has been given the placebo or the drug, or in phase three the existingor 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


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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 arecontrols: 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 ofsurvival 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


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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 adaptationsbecome more common in the population.

Biodiversity and Endemism

Biodiversity: the variety of organisms in an area. This includes:

o Species diversity: number ofdifferent species and abundance of

each species in an area

o Genetic diversity: Variation ofalleles 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.


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2. Count the number of different species AND the number of individuals in

each species. Then use a biodiversity index e.g. Simpsons 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 thesample.

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 youve 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


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Genotype:

o Analyzing an organisms 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 extinctionbecause 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 bestored 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


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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, orvandalism

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 breedingoutside 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 toprevent 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 interestin 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.


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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.

Epic Bio Notes (For A-level)

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