part 1 Flashcards
Why would we use the root tip for investigating mitosis?
It is the location of meristematic tissue (source of stem cells) in a plant, i.e. cells are actively dividing.
Explain why we warm the root tips in hydrochloric acid when preparing a root tip squash.
To break the links between cellulose cell walls in plant cells; this ensures the stain penetrates the cells and binds to the chromosomes.
Which stain would we use to stain chromosomes in a root tip squash?
Acetic orcein.
What is meiosis?
The formation of gametes. Genetically unique with half the genetic information of a somatic cell.
Describe how meiosis produces genetic variation in the gametes produced.
Crossing over in prophase I; independent assortment in metaphase I; independent assortment in metaphase II.
Describe the difference between anaphase I and anaphase II.
In anaphase I, a homologous pair of chromosomes is separated so the chromosome number halves (2 haploid cells made); in anaphase II, sister chromatids of each chromosome are separated so chromosome number stays the same (haploid number maintained).
In which stage of meiosis is the chromosome number halved?
Anaphase/telophase I.
Explain why genetic variation is important for a population of organisms.
More likely that some individuals are adapted to a change in the environment, so the population can survive.
What is differentiation?
The process by which a cell develops to become more distinct in form and function.
Describe and explain how erythrocytes are adapted for their function.
Very small so have a large SA:vol (biconcave shape also ensures this) meaning oxygen can reach all regions inside the cell; well-developed cytoskeleton allows the erythrocytes to change shape and move through very narrow capillaries; no nucleus or organelles so more space for Hb molecules.
Explain why a neutrophil contains many lysosomes.
These contain hydrolytic enzymes which digest pathogens.
Describe and explain how sperm cells are adapted for their function.
Acrosome in head contains enzymes to penetrate the egg follicle during fertilisation; many mitochondria to generate ATP for flagellar movement; large haploid nucleus in head to fertilise haploid ovum.
Describe how guard cells open in sunny conditions.
Light energy –> ATP; ATP used to actively transport potassium ions from epidermal cells into guard cells; water potential of guard cells lowered; water moves in by osmosis and guard cells become turgid.
Describe the purpose of cytoskeleton threads and motor proteins in palisade cells.
Moves the chloroplasts to areas of appropriate light intensity.
Describe how a root hair cell plasma membrane is adapted for transport of mineral ions.
Contains specialised carrier proteins to transport specific mineral ions in by active transport.
Describe how cartilage is adapted for its function.
Connective tissue that contains elastin and collagen fibres; prevents ends of bones from rubbing together.
Define the term tissue.
A group of cells working together to perform a particular function.
State three types of muscle tissue, giving an example of where each is found.
Skeletal - bicep/tricep etc.; smooth - digestive tract, blood vessels; cardiac muscle - heart walls.
Give four features of meristematic cells that means they can differentiate easily.
Thin walls with very little cellulose; no chloroplasts; no large vacuole; divide by mitosis and have the ability to differentiate into many cell types.
Describe the differences between multipotent, pluripotent and totipotent stem cells.
Multipotent - found in bone marrow and can form a range of different cells including blood cells; pluripotent - found in early embryos (embryonic stem cells) and can form all tissue types except extra-embryonic cells; totipotent - found in first 16 cells post-zygote and can form all tissue types including extra-embryonic tissue (e.g. placenta, umbilical cord).
State three characteristics of stem cells.
Undifferentiated; all genes able to be expressed; self-renewing; able to differentiate into any cell type.
State the three main factors that affect the need for an exchange system.
Size, SA:Vol ratio and level of activity.
Explain why smaller organisms have a lower demand for oxygen than larger organisms.
Smaller organisms have a larger SA:V ratio than larger organisms; simple diffusion can be sufficient for unicellular organisms but due to many-layered multicellular organisms, it would be too slow. Multicellular organisms therefore need transport systems.
Describe and explain three features of a good exchange surface.
Large SA (folded walls; provides more space for relevant molecules to pass through); thin, permeable barriers (reduces diffusion distance); good blood supply (keeps high concentration gradients for rapid diffusion).
Describe how human alveoli are adapted to reduce diffusion distances.
Alveolus wall one cell thick; capillary wall one cell thick; walls of alveoli/capillaries contain squamous (flattened) cells; capillaries are in close contact with alveoli walls; capillaries are narrow to restrict RBC movement.
Describe the role of surfactant in alveoli.
Coats the internal surface of the alveoli to reduce cohesive forces between water molecules, preventing collapse.
Describe the mechanism of inspiration.
Diaphragm contracts (moves down and flattens); external intercostal muscles contract to push ribcage up and out; volume of thorax increased and so pressure decreases below atmospheric pressure; air rushes into lungs down a pressure gradient.
Why do alveolar walls contain elastic fibres?
To stretch during inspiration and recoil, pushing air out, during expiration.
Which tissue type comprises alveolar walls?
Squamous epithelium.
The trachea is lined with ciliated epithelial tissue and goblet cells. Describe the functions of these.
Goblet cells produce mucus onto the tracheal lining, trapping dust and microorganisms. The cilia then beat and move the mucus away from the lungs and towards the throat.
The trachea and bronchi are lined with cartilage. Describe why.
C-shaped rings of cartilage line these tubes, preventing collapse during inspiration. The C-shape allows food to pass down the oesophagus behind the trachea.
Describe how the nasal cavity is adapted for exchange.
Large SA with a good blood supply, warming air to body temperature; lined with hair (which secretes mucus) to trap dust and MOs, protecting from infection; moist surfaces to increase the humidity of the incoming air, reducing evaporation from exchange surfaces.
Describe the roles of smooth muscle and elastic tissue in the airways.
Smooth muscle can contract to constrict airways (not under conscious control, i.e. involuntary); elastic fibres elongate smooth muscle again, recoiling the airway to its original shape and size (dilates airway).
Describe precautions that must be taken when using a spirometer.
Subject should be free of asthma; there should be no air leaks in the apparatus; mouthpiece should be sterilised; soda lime should be fresh and functioning.
Describe what is meant by ‘vital capacity’ and state the factors that it depends upon.
The maximum volume of air that can be moved by the lungs in one breath; measured by taking one deep breath and expiring all the possible air from the lungs. Depends on: size (height) of person; age/gender; exercise levels.
State the usual range for vital capacity.
2.5 - 5.0 dm3.
Describe what is meant by ‘inspiratory reserve volume’.
The maximum volume of extra air you can breathe in forcibly (vital capacity - tidal volume - ERV).
Describe what is meant by ‘expiratory reserve volume’.
The maximum volume of extra air you can breathe out forcibly (vital capacity - tidal volume - IRV).
Describe what is meant by ‘residual volume’ and state the standard volume.
The volume of air that remains in the lungs even after forced expiration, i.e. the air that remains in the airways and alveoli (usually 1.5 dm3).
Describe what is meant by ‘tidal volume’ and state a typical figure.
Volume of air moved in and out with each breath at rest. A normal value would be 0.5 dm3 (500cm3).
What is the difference between ‘ventilation rate’ and ‘breathing rate’?
BR = no. of breaths taken per min; VR = total volume of air inhaled per min.
State the equation for ventilation rate.
Ventilation rate = tidal volume x breathing rate (breaths per minute).
The normal breathing rate of a healthy 50 year old woman is 18 breaths per minute and her tidal volume is 500 cm3. During strenuous exercise, her ventilation rate increases to 45 000 cm3min-1 and she is breathing 30 times a minute. Calculate her tidal volume during this exercise and state how much higher than normal this figure is.
TV = 1500 cm3 …1 dm3 higher than normal.
Most bony fish have 5 pairs of gills which are covered by a bony flap, known as the …? What is the function of this bony flap?
Operculum; protects the gills and ensures a constant flow of water.
Describe the structure of gills in bony fish.
Two rows of gill filaments; these are slender branches of tissue known as primary lamellae and are attached to a bony arch. Each gill filament is folded into secondary lamellae providing a very large surface area.
Describe ventilation in bony fish.
Buccal cavity (mouth) can change volume; floor of mouth moves downwards, drawing water into the buccal cavity; mouth closes and water is pushed through the gills. As water is pushed from the buccal cavity through the gills, the operculum moves outwards.
How is air supplied to respiring tissues in an insect?
Tracheal system.
How does air enter the tracheal system in an insect?
Spiracle.
The ends of tracheoles in insects are filled with tracheal fluid. What is the function of this fluid?
Gaseous exchange occurs between air in tracheole and the tracheal fluid.
When an insect is active, what changes occur in the insect to increase their oxygen supply?
Tracheal fluid can be withdrawn into the body fluid to increase the surface area of the tracheole wall exposed to air.
Describe three features of an effective transport system.
A fluid to carry nutrients/oxygen/wastes around the body (blood); a pump to create pressure that will push the fluid around the body (heart); exchange surfaces (capillaries).
Describe three disadvantages of single circulatory systems, as seen in fish.
Blood pressure drops as blood passes through the gill capillaries; blood flows slowly through as it is under low pressure; the rate of delivery of oxygen/nutrients to respiring tissues is limited (and removal of CO2 and urea).
Explain why fish do not need as much energy as mammals.
They are not as metabolically active as mammals as they do not maintain their body temperature.
Describe what is meant by the term open circulation.
Blood is not always held in vessels, but it circulates throughout the body cavity and the tissues and cells bathe directly in blood.
State two disadvantages of open circulatory systems.
Blood pressure is low and blood flow is therefore slow; circulation can be affected by body movements (or lack of).
State four advantages of closed circulation over open circulation.
Blood travels at higher pressure and therefore flow is faster; oxygen/nutrients supplied and CO2/urea removed more quickly; transport is independent of body movements.
What is the inner tissue lining of a blood vessel called? What is its role?
Endothelium; reduced friction with the flowing blood.
Describe the three structural layers of an artery.
Tunica intima - thin layer of elastic tissue which allow walls to stretch and recoil (opposes muscle); tunica media - thick layer of smooth muscle; tunica adventitia - thick layer of collagen and elastic tissue providing strength to withstand the high pressure and recoiling against the muscle.
What is the role of arterioles?
Take blood from artery to capillary; they have a layer of smooth muscle which contracts restricting and slowing blood flow.
Describe how capillaries are adapted for exchange.
Narrow lumen (squeezes red blood cells against walls so transfer of oxygen is better to the tissues); walls consist of single layer of endothelial cells (reduces diffusion distance); walls are permeable (allows blood plasma and dissolved substances to leave the blood).
Describe the function of a venule.
Takes blood from the capillaries to the veins.
Describe how veins are adapted to carry blood back to the heart.
Wide lumen to ease blood flow; thin layers of elastic/muscle/collagen in walls as no need to stretch and recoil; valves to prevent backflow of blood.
Where is hydrostatic pressure created of the blood created?
In the ventricles of the heart.
What is oncotic pressure?
The pressure created by the osmotic effects of the solutes.
What substances might affect the oncotic pressure of the blood?
Dissolved solutes such as mineral ions, sugars and proteins.
State the cell types that are most likely to be found in blood plasma, tissue fluid and lymph.
Blood plasma - red blood cells, neutrophils, lymphocytes; tissue fluid - neutrophils (especially during infection); lymph - lymphocytes.
Why can proteins known as plasma proteins not leave the blood plasma?
They are too large to pass between the squamous cells of the capillary wall.
Why can neutrophils enter the tissue fluid but erythrocytes cannot?
Neutrophils can change shape very easily (multilobed nucleus) and squeeze themselves between cells. Erythrocytes cannot change shape as much.
Describe the role of the lymph fluid.
A system of tubes that returns excess tissue fluid to the blood system.
How does tissue fluid facilitate exchange of substances to body cells?
Tissue fluid surrounds body cells so exchange occurs across plasma membranes.
Describe the simple structure of haemoglobin.
Four subunits (each with a polypeptide chain and a haem group); haem groups each contain an Fe2+ ion at the centre; iron ions can attract and hold an oxygen molecule.
What is the process known as by which oxyhaemoglobin releases its oxygen to respiring cells?
Dissociation.
What is the main difference between foetal haemoglobin and adult haemoglobin?
It has a higher affinity for oxygen than adult haemoglobin.
Describe three ways in which carbon dioxide is transported.
5% dissolved directly in the plasma; 10% directly with haemoglobin in the form of carbaminohaemoglobin; 85% in the form of hydrogencarbonate ions.
Describe the formation of hydrogencarbonate ions.
Carbon dioxide from the blood plasma diffuses into RBCs and combines with water to form carbonic acid (catalysed by carbonic anhydrase); carbonic acid then dissociates into hydrogencarbonate ions and protons.
Describe how the charge inside a RBC is maintained when hydrogencarbonate ions diffuse into the plasma.
Chloride ions move into the RBCs from the plasma (chloride shift).
Describe how the pH inside a RBC is buffered as hydrogen ions build up inside, making the RBC very acidic.
Hydrogen ions are taken out of solution and combined with haemoglobin to form haemoglobinic acid (HHb).
What is the net result of the Bohr effect?
More oxygen is released where more carbon dioxide is produced in respiration.
With reference to protein structure, explain how increasing hydrogen ion levels affects haemoglobin.
More hydrogen ions –> lower pH (more acidic cytoplasm); tertiary structure of Hb altered which reduces its affinity for oxygen.
What is the purpose of semilunar valves?
To prevent backflow of blood from arteries to the ventricles.
What happens when hydrogen ions build up inside the RBC?
Hydrogen ions are taken out of solution and combined with haemoglobin to form haemoglobinic acid (HHb).
How do increasing hydrogen ion levels affect haemoglobin?
More hydrogen ions lead to lower pH (more acidic cytoplasm); the tertiary structure of Hb is altered, reducing its affinity for oxygen.
Why is the left ventricular wall thicker than the right?
Blood is pumped through the aorta and needs sufficient pressure to overcome the resistance of the systemic circulation.
Why are there many mitochondria in cardiac muscle?
To supply energy for contraction.
What is the purpose of intercalated discs between adjacent muscle cells?
Ensures an even, synchronised contraction.
Briefly outline the events of atrial systole.
Left and right atria contract together; blood is squeezed from the atria through the atrioventricular valves into the ventricles, down a pressure gradient.
Briefly outline the events of ventricular systole.
Ventricular blood pressure rises quickly to a level above the arteries; semilunar valves open and blood rushes out of ventricles into the arteries.
Briefly outline the events of diastole.
Once ventricular contraction is complete, heart muscle starts to relax, heart starts to fill with blood again and semilunar valves close.
What is meant by the term myogenic?
Cardiac muscle can initiate its own contractions.
What tissue is responsible for initiating the heartbeat?
Sinoatrial node (SAN).
What tissue propagates the electrical signal from the atria to the ventricles?
Atrioventricular node (AVN).
Why is there a delay before the AVN depolarises the ventricular walls?
To allow the atria to finish contracting.
Describe the role of the Purkyne tissue.
Specially adapted muscle fibres that conduct the wave of excitation from the AVN down the septum to the ventricles.
What terms describe a slow and a fast heart rate?
Bradycardia; tachycardia.
What happens in atrial fibrillation?
Atria beat more frequently than ventricles, meaning no clear P wave can be seen on ECG.
What is an ectopic heart beat?
An early ventricular beat.
What are the two major vascular tissues in plants?
Xylem - water, soluble mineral ions (upwards); phloem - assimilates (up or down).
What tissue is found between the xylem and phloem?
Meristematic tissue (source of stem cells).
What is the purpose of parenchyma cells in xylem tissue?
To separate and support the vessels (act as packing tissue).
What is the purpose of lignin in xylem vessels?
Strengthens vessel wall and prevents collapse.
How do bordered pits form and what is their purpose?
Where lignification is incomplete, leaving gaps in the cell wall; they allow water to leave one vessel and pass into the next.
Describe three adaptations of xylem vessels that relate structure to function.
1) Dead cells aligned end to end to form a continuous column; 2) Tubes are narrow for effective capillary action; 3) Bordered pits allow sideways movement of water.
What two components of phloem tissue are concerned with transport?
Sieve-tube elements and companion cells.
Why do sieve tube elements contain no nucleus?
Allows space for mass flow of sap to occur.
How are companion cells adapted for active loading?
Many mitochondria to produce ATP.
Describe two major pathways taken by water to move between cells.
Apoplast - through spaces in cell walls; symplast - moves through cytoplasm via plasmodesmata.
What allows water to move through cells via the symplast pathway?
Different water potential of cytoplasm of adjacent cells; water moves by osmosis.
What allows water to move continuously via the apoplast pathway?
Cohesion, by diffusion.
Why does the presence of starch in the endodermis suggest an active process?
Starch acts as a store of sugars, which can be released for active processes.
What is the Casparian strip?
A band of waterproof, waxy suberin around each endodermis cell.
Explain the significance of the Casparian strip.
Locks the apoplast pathway, forcing water and dissolved minerals to pass through the selectively permeable membrane.
Describe how water is lost via stomata.
Water vapour in higher concentration in air spaces than outside; water diffuses down the water vapour potential gradient.
How do light intensity, humidity, and wind speed affect transpiration?
Increased light intensity increases rate; increased humidity decreases rate; increased wind speed increases rate.
What precautions should be taken to ensure no air bubbles in the potometer setup?
Set up under water; cut stem under water.
Calculate the rate of transpiration if the meniscus moves 45mm in 5 minutes.
7.1mm3/min.
Describe how water moves up the stem via the transpiration pull.
Loss of water by evaporation creates tension that pulls the column of water up the xylem.
What property of water causes cohesion?
The polarity of the water molecule, producing hydrogen bonds.
Define the term translocation.
Transport of assimilates from source to sink.
State two sinks for translocation in a plant.
Roots growing or actively uptaking mineral ions; actively dividing meristematic tissue.
What is the difference between active loading and active transport?
Active transport is movement against concentration gradient using ATP; active loading involves active transport and facilitated diffusion.
Describe the role of hydrogen ions in active loading.
Hydrogen ions create a concentration gradient, allowing sucrose to move back into companion cells through cotransport.
Why is sucrose transported in phloem and not glucose?
Sucrose is more stable and less likely to be metabolised during transport.
How does sucrose move from companion cells into sieve tube elements?
Increasing sucrose concentration causes water to move into companion cells, building up turgor pressure.
What principle does mass flow work on in sieve tubes?
Turgor pressure difference between source and sink.
What principles does phloem unloading work on?
Diffusion of sucrose into surrounding cells or conversion into glucose.
Describe three adaptations of marram grass (xerophyte).
Leaf rolled to trap humid air; thick waxy cuticle to reduce evaporation; stomata in pits to reduce air movement.
What does it mean for cacti to be succulents?
They store water in their stems, which become fleshy and swollen.
Why is it advantageous for some xerophytes to have low water potential in leaf cells?
Reduces evaporation from cell surfaces.
Describe two adaptations of roots for arid conditions.
Roots could be very long to reach deep water; roots could be widespread to absorb water from a large area.
What is classification?
The process of putting living things into groups.
Why do scientists classify organisms?
It simplifies identification, predicts characteristics, and identifies evolutionary links.
What is taxonomy?
A hierarchical grouping system, where each group is subdivided into smaller groups.
What are the eight taxonomic groups in order?
Domain; Kingdom; Phylum; Class; Order; Family; Genus; Species.
What is the binomial naming system?
A naming system using two names: the genus and species, with the genus capitalised.
Why is the binomial naming system important?
It provides a universal scientific name for species, avoiding confusion from common names.
What are the 5 kingdoms in classification?
Prokaryotae, protoctista, fungi, plantae, animalia.
What are the general features of prokaryotae?
- Unicellular
- No nucleus or membrane bound organelles
- A ring of naked DNA
- No feeding mechanism.
What are the general features of protoctista?
- Mainly unicellular
- Nucleus and membrane bound organelles
- Some have chloroplasts.
- Nutrients acquired by photosynthesis or ingestion.
What are the general features of fungi?
- Unicellular or multicellular
- A nucleus and membrane bound organelles
- A cell wall made of chitin.
What are the general features of plantae?
- Multicellular
- A nucleus and membrane bound organelles
- Cell wall made from cellulose
- Autotrophic.
What are the general features of animalia?
- Multicellular
- A nucleus and membrane bound organelles
- No cell wall
- Heterotrophic.
What are the 3 domains of classification?
Bacteria, archaea, eukarya.
Why are 3 domains preferred to 5 kingdoms?
1) Fits better with phylogeny; 2) Key differences between prokaryotes and eukaryotes; 3) All eukaryotic kingdoms have a nucleus.
What is the difference between eukarya, bacteria, and archaea in terms of ribosomes?
Eukarya have 80s; Bacteria and Archaea have 70s.
What is the difference between eukarya, bacteria, and archaea in terms of RNA polymerase?
Eukarya have 12 proteins; Bacteria have 8-10; Archaea have 5.
In the new system of classification, what are the 6 kingdoms?
Eubacteria, archaebacteria, protoctista, fungi, plantae, animalia.
Which group has been divided to form eubacteria and archaebacteria?
Prokaryotae.
What is the difference between the habitats of archaebacteria and eubacteria?
Archaebacteria live in extreme conditions; Eubacteria are found in all environments.
What is phylogeny?
The name given to the evolutionary relationships between organisms.
What are phylogenetics?
The study of the evolutionary history of groups of organisms.
What is a phylogenetic tree?
A diagram showing the evolutionary history of groups of organisms.
What are the advantages of phylogenetic classification?
Connects groups based on relationships rather than characteristics.
What is evolution?
The theory that describes how organisms change over many years through natural selection.
What did Darwin observe to support his theory of evolution?
Organisms best suited to the environment are more likely to survive and reproduce.
What are the 3 main sources of evidence for evolution?
Paleontology; comparative anatomy; comparative biochemistry.
What is paleontology?
The study of fossils and what they can tell us about the Earth’s past.
What evidence for evolution is shown in the fossil record?
Fossils of simple organisms in oldest rocks, more complex organisms in youngest rocks.
Why is the fossil record not complete?
- Many organisms are soft-bodied and decompose.
- Conditions aren’t right for fossilisation.
What is comparative anatomy?
The study of similarities and differences in the anatomy of living species.
What is a homologous structure?
A structure that appears differently in different organisms but has the same underlying structure.
Why is the fossil record not complete?
- Many organisms are soft bodied and therefore decompose
- The conditions aren’t right for fossilisation
- Fossils may be destroyed by the Earth’s movement
What is a homologous structure?
A structure which appears differently in different organisms, but has the same underlying structure, eg the pentadactyl limb of vertebrates.
What do homologous structures provide evidence for?
Divergent evolution
What is divergent evolution?
The description of different organisms evolving from a common ancestor.
What is comparative biochemistry?
The study of similarities and differences in the proteins and other molecules that control life processes.
How are molecules used in comparative biochemistry?
Some molecules are important for all life and remain highly conserved (don’t change much). Slight changes in these molecules over time and between species can be used to identify relationships. The greater the similarity, the closer the relationship.
Which molecules can be used in comparative molecular biochemistry?
Cytochrome C (used in respiration)
Ribosomal RNA.
What are the two types of variation between organisms?
Interspecific and intraspecific
What is interspecific variation?
Variation between organisms of different species.
What is intraspecific variation?
Variation between organisms of the same species.
What are the causes of variation?
1 - Genetic
2 - Environmental
What are the causes of genetic variation?
1 - Alleles
2 - Mutations
3 - Meiosis
4 - Sexual reproduction (2 partners)
5 - Chance
How do alleles cause genetic variation?
Alleles are variant forms of a gene. Different alleles produce different effects and different characteristics. Individuals of a species may inherit different alleles.
How do mutations cause genetic variation?
Mutations are changes to the DNA sequence, and therefore the proteins the genes code for. This can affect the physical and metabolic characteristics.
How does meiosis cause genetic variation?
Meiosis is the formation of gametes. During this process the independent assortment of chromosomes and the crossing over (creating chiasmata) occurs. This leads to genetically unique sex cells.
How does sexual reproduction (2 partners) cause genetic variation?
During sexual reproduction, the offspring inherits genetics from both parents, therefore being their own different organism.
How does chance cause genetic variation?
During sexual reproduction, any 2 of the many gametes produced could end up combining. This is random fertilisation, it is why siblings differ from one another.
Why is there much more variation in sexually reproductive organisms than those which reproduce asexually?
Meiosis, sexual reproduction (2 partners) and chance are all aspects of sexual reproduction. There is therefore more likelihood of variation through this process. Asexual reproduction results in the creation of clones.
Are animals or plants more likely to be affected by the environment and cause variation? Why?
Plants, as they lack mobility.
Give an example of a purely environmental variation.
The presence or absence of scars. These cannot be inherited.
In most cases, what causes variation within a population?
Both genetic and environmental causes.
Give an example of a characteristic that can be affected by both genetic and environmental factors.
Height - you can inherit the genes to allow you to grow, but if your diet is poor, you may not be able to reach your potential height.
Skin colour - your skin colour is determined by genes, though exposure to sunlight and UV rays will darken the skin.
It is hard to separate genetic and environmental factors from causing variation. What investigations are done to allow better understanding between nature and nurture?
Twin studies, especially twins who have been separated and brought up in different environments.
Into which 2 groups can data on characteristic variation be sorted?
Discontinuous and continuous variation.
What is another term for discontinuous variation?
Discrete variation
What is discontinuous variation?
Variation that can only be put into particular categories, or results in certain values.
Give an example of discontinuous variation.
- An animal’s sex,
- The shape of a bacteria
- Human blood group
What causes discrete variation?
A characteristic purely determined by genetics, typically a single gene.
How is discontinuous variation displayed graphically?
Using a bar chart.
What is continuous variation?
A characteristic that can take any value within a range. There is a gradual change from one extreme to another.
What is an example of continuous variation?
- Height
- Mass
What causes continuous variation?
- Multiple genes determining that characteristic (polygenes) also influenced by the environment.
How is continuous variation displayed graphically?
- Collected on a frequency table
- Histogram drawn
- Curve drawn onto graph
Continuous variation typically shows what distribution?
Normal distribution.
What is normal distribution?
Data that creates a bell curve when plotted.
What are the characteristics of normal distribution?
- Mean, median and mode are the same
- Distribution is a bell curve, symmetrical about the mean
- 50% of values are less than the mean, and 50% greater
- Most values are close to the mean, the values at the extremes are low.
What is standard deviation?
A measure of how spread out the data is.
What does the variation look like if there is a high standard deviation?
A large amount of variation.
What does the variation look like if there is a low standard deviation?
A small amount of variation.
In normal distribution, what are the typical values for the first 3 standard deviations?
1 SD - 68% of values
2 SD - 95% of values
3 SD - 99.7% of values
What do the symbols in the standard deviation formula stand for?
σ - Standard Deviation
∑ - Sum of (add all the numbers together)
x - measured value
x̅ - mean value
n - total number of values
What is the Student’s t test used for?
Comparing the averages of data values between two populations. (Are two populations statistically similar or different?)
What is Spearman’s rank correlation coefficient used for?
Considering the relationship between two sets of data. (Is there a correlation or not, if so is it positive or negative?)
What are the purpose of statistical tests?
To determine whether any relationship or outcome is due to chance, or an outside factor affecting the organisms. It determines the significance of the data.
What is a null hypothesis in a Student’s t test?
The prediction that there is no significant difference between the populations. Any observed difference is due to chance.
What is a null hypothesis in a Spearman’s rank?
The prediction that there is no significant relationship between the data. Any observed relationship is due to chance.
What are the degrees of freedom in a Student’s t test?
It describes how much data was collected. It is calculated by (n1 + n2) - 2.
How do you determine significance in a Student’s t test?
The value of ‘t’ is looked up in the Student’s t test significance tables comparing the probability value to the degrees of freedom. For the data to be significantly different from chance alone, the value of ‘t’ must be lower than a probability of 5% or 0.05.
What do the probability values in the significance tables mean?
How likely the effect observed is down to chance. We use the 5% (0.05) probability value.
How do you determine significance in a Spearman’s rank?
The value of the correlation coefficient is looked up in the Spearman’s rank significance tables comparing the probability value to the number of values, ‘n’. For the data to be significantly different from chance alone, the value of ‘t’ must be lower than a probability of 5% or 0.05.
What are adaptations?
Characteristics that allow an organism to survive and reproduce in its environment.
What are the 3 types of adaptation?
Anatomical; behavioural; physiological.
What is an anatomical adaptation?
A physical feature, internal or external.
What is a behavioural adaptation?
The way an organism acts, either inherited or learned from parents.
What is a physiological adaptation?
A process that goes on inside an organism.
Give an example of an anatomical adaptation.
Body coverings - such as a shell, hair or feathers
Camouflage - to blend in with the environment so as not to be seen
Teeth - the shape and type allows different food to be eaten
Mimicry - copying another organism’s appearance or sound to fool predators
How is Marram grass adapted to stop transpiration?
Curled leaves - minimise exposed area of leaves
Hairs on inside - trap moist air increasing humidity
Sunken stomata - less likely to lose water
Thick waxy cuticle - reduces water loss through evaporation
Give an example of a behavioural adaptation.
Survival - eg playing dead
Courtship - eg mating dances
Seasonal - eg migration or hibernation
What are the two main types of behavioural adaptation?
Innate; learned.
What is an innate behaviour?
Instinctive, it is inherited through genes, e.g. avoiding light, building webs.
What is a learned behaviour?
Developed through experience and observation, e.g. use of tools, language.
Give an example of physiological adaptations.
Poison production
Antibiotic production
Water storing
Reflexes
Homeostasis
What is convergent evolution?
Where two unrelated species develop traits or characteristics. Same function, but different genetic origin.
Why does convergent evolution occur?
The unrelated organisms live in similar environments and are experiencing similar selection pressures.
What is natural selection?
The process by which organisms best suited to their environment survive and reproduce, passing on their characteristics to their offspring through their genes.
What are the steps involved in natural selection?
1 - Organisms within a species show variation;
2 - Organisms best adapted to a selection pressure are more likely to survive and reproduce;
3 - Successful organisms pass the allele encoding the advantageous characteristic to their offspring;
4 - This process is repeated each generation, and the frequency of the advantageous allele increases;
5 - Over a very long time period, this process may lead to the evolution of a new species.
What is a selection pressure?
Factors which affect an organism’s chance of survival or reproductive success.
What are examples of selection pressures?
Predation;
Competition (mates / resources);
Disease;
Etc.
What is biodiversity?
The variety of living organisms in an area.
Why is biodiversity important?
Biodiversity allows a balanced ecosystem. Many organisms rely on one another; they are interconnected.
Why do humans rely on balanced ecosystems?
They supply us with oxygen, food, and other materials for survival.
How can human activities lead to a reduction in biodiversity?
Farming, clearing land for housing can remove biodiversity.
What are the 3 ways of measuring biodiversity?
1 - Habitat biodiversity;
2 - Species biodiversity;
3 - Genetic biodiversity.
Why is it important to measure biodiversity?
Supports conservation, giving a baseline for scientists to monitor changes.
What is habitat biodiversity?
This refers to the number of habitats found within an area. In general, the greater the habitat biodiversity, the greater the species biodiversity.
What is species biodiversity?
A measure of the species present within an area. Made of 2 components: 1 - Species richness; 2 - Species evenness.
What is species richness?
The number of different species living within an area.
What is species evenness?
A comparison of the numbers of individuals of each species in a community.
What is a community?
All of the populations of living organisms in a particular habitat.
What is genetic biodiversity?
This refers to the variety of genes making up an organism. It also takes into account the different alleles that exist for those genes. This is what creates variation within a species.
Why is genetic variation important?
Greater genetic variation within a species allows for better adaptation to a changing environment.
What is sampling?
Taking measurements of a limited number of organisms of an area.
Why is sampling important?
It is often impossible to count / measure all of the organisms in a particular area.
What is sampling used for?
It can be used to: 1 - estimate the number of organisms in an area; 2 - estimate a particular characteristic of an organism.
What are the 2 ways sampling can be carried out?
Random and non-random.
What is random sampling?
Selecting individuals by chance, each individual has an equal likelihood of being selected.
How is random sampling carried out?
A random number generator is used. The scientist is not involved in choosing at all. Often 2 tape measures are laid out as a grid, random numbers generate coordinates. Samples are taken here.
What is non-random sampling?
This is where the sample is chosen, or selected.
What are the 3 main types of non-random sampling?
1 - Opportunistic;
2 - Stratified;
3 - Systematic.
What is opportunistic sampling?
Weakest form of sampling. May not be representative of the population. Measures the organisms conveniently available.
What is stratified sampling?
Separating populations into strata (sub-groups). e.g. male / female. Random sampling is done on these proportional to their size.
What is systematic sampling?
Different areas within a habitat are defined, and then sampled separately. e.g. the change in organisms as you move inland from the sea.
What are two techniques that could be used in systematic sampling?
Line transect and belt transect.
What is a line transect?
A line is marked between two points. Samples are taken at specified points. Everything touching the line is counted.
What is a belt transect?
2 parallel lines are marked, and samples are taken in the area between the lines. More information gathered than with a line transect.
What is an interrupted belt transect?
A line transect is drawn. A quadrat is placed at regular intervals. A sample is taken from within the quadrat.
What is reliability?
A measure of how representative of the organisms present in the habitat the sampling is. How accurate the sampling is.
What can decrease the reliability of the sampling being done?
1 - Sampling bias
2 - Chance
What is sampling bias?
Accidental or deliberately choosing a particular area to sample. This effect is reduced by random sampling.
What is chance?
The organisms selected may not be representative of the whole population. Chance cannot be removed, but its effect can be reduced by having a large sample size.
What are the techniques used in collecting live animal samples?
1 - Pooter;
2 - Sweep nets;
3 - Pitfall traps;
4 - Tree beating;
5 - Kick sampling.
How is a pooter used?
It collects small insects by drawing them into a holding chamber by sucking on a mouthpiece.
How are sweep nets used?
By sweeping long grass, they collect insects.
How are pitfall traps used?
They collect small crawling invertebrates. A hole is dug in the ground which they fall into and can’t climb out of.
How is tree beating used?
A large white cloth is laid under a tree or bush. This collects invertebrates knocked off as the tree is shaken.
How is kick sampling used?
The riverbed is gently kicked to disturb substrate. A net is held just downstream to collect organisms released into the water.
How are plants generally sampled?
Using a quadrat. Either frame quadrat or point quadrat.
What is a point quadrat and how is it used?
A frame with a horizontal bar. Down which long pins can be dropped. Any plant touching the pin will be recorded.
What is a frame quadrat?
A square frame, divided into smaller equal sections. The type and number of each species within a section is recorded.
What is the most valid way of sampling an area?
Random sampling using quadrats.
What is the most valid way of sampling the change in distribution of species across an area of land?
Laying quadrats along a line or belt transect.
How is species richness measured?
A variety of sampling techniques is used to identify all species present in a habitat. A list is created and the total number calculated. An identification key may be used to accurately identify organisms.
What is a quadrat?
A square frame, divided into smaller equal sections. The type and number of each species within a section is recorded.
How is species richness measured?
A variety of sampling techniques is used to identify all species present in a habitat. A list is created and the total number calculated.
How is species evenness measured?
A variety of sampling techniques is used to identify both the species and number of individuals in those species present in a given habitat.
What are the different types of data that can be collected using frame quadrats?
1 - Density; 2 - Frequency; 3 - Percentage cover.
How and when is density measured using a frame quadrat?
This is an absolute measure of individual plants in a specific area. E.G. count the number of dandelions in 1m2 gives density per square meter.
How and when is frequency measured using a frame quadrat?
Count the number of squares in which they are present. Give this as a percentage of the total number of squares in the quadrat.
How and when is percentage cover measured using a frame quadrat?
An estimation of the cover is done by eye, using the quadrat and its squares as a guide.
How is the use of quadrats made more reliable?
Multiple samples are taken from an area. The mean is then calculated.
How is a mean calculated?
Add the individual results, then divide by the number of repeats.
How is animal population size estimated?
Using capture - mark - release - recapture.
Why is measuring animal population size difficult?
The animals move about, they may be hidden, they go through different stages of development, so may be hard to identify.
What are abiotic factors?
Non-living conditions in a habitat.
What are common abiotic factors?
- Wind speed
- Light intensity
- Humidity
- pH
- Temperature
- Oxygen content in water.
What formula is used to calculate biodiversity?
Simpson’s index of biodiversity.
In Simpson’s index of diversity, what do D, n and N stand for?
D - Is the measure of diversity; n - is the sum of organisms of a particular species; N - is the total number of organisms of all species.
When D is calculated in the Simpson’s index of diversity, what does it mean?
The value falls between 0 and 1. 0 is no diversity, 1 is infinite diversity.
What are the characteristics of a low biodiversity habitat?
1 - Few successful species; 2 - stressful / extreme; 3 - Species have very specific adaptations; 4 - Simple food webs; 5 - Environmental change has a major effect on the ecosystem.
What are the characteristics of a high biodiversity habitat?
1 - Many successful species; 2 - Benign environment; 3 - Species have few specific adaptations; 4 - Complex food webs; 5 - Environmental change has a relatively minor effect on the ecosystem.
What is genetic biodiversity?
This refers to the variety of genes making up an organism.
Why is genetic biodiversity important?
Species with greater genetic biodiversity are more likely to survive changes to their environments.
What are the factors that affect genetic biodiversity?
1 - Mutations; 2 - Interbreeding (gene flow); 3 - Selective breeding (artificial selection); 4 - Captive breeding; 5 - Rare breeds; 6 - Artificial cloning; 7 - Natural selection; 8 - Genetic bottlenecks; 9 - The founder effect; 10 - Genetic drift.
How do mutations affect the genetic biodiversity?
They change the DNA, and can create new alleles.
How does interbreeding (gene flow) change the genetic biodiversity?
Individuals moving from one population to another and breeding will cause alleles to transfer between populations.
How does selective breeding (artificial selection) change the genetic biodiversity?
Only a few individuals are selected from a population to breed due to their advantageous characteristics.
How does captive breeding change genetic biodiversity?
Only a few individuals are present in zoos or conservation centers, the gene pool is relatively small.
How do rare breeds change genetic biodiversity?
Selective breeding has produced a breed of domestic animal/plant which is no longer popular.
How does artificial cloning change genetic biodiversity?
Cloning animals and plants produces genetically identical organisms.
How does natural selection change genetic biodiversity?
Species evolve to contain the alleles which code for advantageous characteristics.
How do genetic bottlenecks change genetic biodiversity?
Few individuals from a population survive a catastrophic event.
How does the founder effect change genetic biodiversity?
A small number of individuals start a new population and are genetically isolated.
How does genetic drift affect genetic biodiversity?
Due to the random nature of alleles being passed on to subsequent generations, the frequency of a particular allele can vary.
What are polymorphic genes?
Genes which have more than one allele.
Why are most genes not polymorphic?
By having a single allele for most genes, the basic structure of an individual within a species remains consistent.
How can we measure genetic biodiversity?
By measuring the proportion of genes that are polymorphic.
What is the locus of a gene?
The position of the gene on a chromosome.
How does the proportion of polymorphic gene loci relate to genetic biodiversity?
The greater the proportion of polymorphic gene loci, the greater the genetic biodiversity within the population.
Describe one way of how deforestation can affect biodiversity.
Trees’ species diversity decreases; habitats destroyed, leading to decline in animal species population/diversity.
Describe one way of how agriculture can affect biodiversity.
Deforestation; hedgerow removals, destroying habitats of small animals.
Describe one way of how climate change can affect biodiversity.
Global warming leading to habitats or food sources destroyed.
Give three reasons for maintaining biodiversity.
Aesthetic reasons; economic reasons; ecological reasons.
Define ‘keystone species’.
Species that are essential for maintaining biodiversity.
What is the difference between ‘in situ’ and ‘ex situ’ conservation?
In situ = within natural habitat (e.g. wildlife reserves); ex situ = out of natural habitat (e.g. zoos).
What is the IUCN?
The IUCN updates conservation status of threatened species.
What is the CITES?
A treaty that regulates the international trade of wild species.
What is the Rio Convention?
Made up of 3 parts - sustainable development, stabilise greenhouse gas concentration, combat desertification.
What is the Countryside stewardship scheme?
UK conservation scheme to make conservation a part of normal farming and land management practice.
State the kingdom of organism that causes tuberculosis.
Bacteria.
State the kingdom of organism that causes Black Sigatoka.
Fungi.
State the kingdom of organism that causes Athlete’s foot.
Fungi.
State the kingdom of organism that causes malaria.
Protoctists.
State the kingdom of organism that causes blight.
Protoctists.
State the kingdom of organism that causes ringworm.
Fungi.
State the kingdom of organism that causes ring rot.
Bacteria.
State the kingdom of organism that causes bacterial meningitis.
Bacteria.
Give one plant disease caused by viruses.
Tobacco mosaic virus.
Give one plant disease caused by bacteria.
Ring rot.
Give one plant disease caused by fungi.
Black Sigatoka.
State three factors that would affect the speed of disease transmission in plants.
Overcrowding; poor mineral nutrition; damp, warm, humid conditions.
State how the influenza virus is most likely to be transmitted between different humans.
Respiratory droplets (inhalation).
State four different types of vector that can be used to transmit a communicable disease.
Water; animals; wind; humans.
State three passive physical defences that prevent plants being infected by a pathogen.
Bark; waxy cuticle; thorns.
State three active physical defences a plant would employ against an invading pathogen.
Callose synthesised and deposited between plasma membrane and cell wall; lignin added to cell walls.
State three chemical defences a plant would employ against an invading pathogen.
Antibacterial compounds like phenols; terpenes; hydrolytic enzymes.
Describe the role of the skin as a primary non-specific defence.
Dead outer layer of keratin prevents pathogen entry; skin flora outcompete pathogens.
Describe the role of mucous membranes as a primary non-specific defence.
Mucus traps pathogens and contains lysozymes.
Which enzyme catalyses the conversion of prothrombin to thrombin?
Thromboplastin (thrombokinase).
Describe the role of thrombin in the clotting process.
Causes the conversion of soluble fibrinogen into insoluble fibrin fibres.
Describe the process of inflammation as a secondary non-specific response.
Mast cells release histamines; histamines increase permeability of capillaries.
Describe the process of phagocytosis.
Phagocyte engulfs pathogen into a phagosome; lysosomes fuse with phagosome.
Describe how macrophages process antigens for presentation on their cell surface membrane.
Antigen fragments combined with MHC.
What name is given to small protein molecules that act as cell-signalling compounds?
Cytokines.
Describe how neutrophils are specialised for their role.
Plasma membrane contains receptors for opsonins.
Opsonins are non-specific. Explain why.
Opsonins can attach to many types of pathogen and help the process of phagocytosis.
Where do B lymphocytes and T lymphocytes mature?
Bone marrow and thymus respectively.
What is meant by the term ‘autoimmunity’ and give two examples of autoimmune diseases.
Destruction of self-tissue; rheumatoid arthritis, lupus.
What is the role of T regulatory cells?
Dampen down the immune response.
Describe how an antigen presenting cell leads to large numbers of T helper cells.
APC binds specifically to a Th cell.
Describe how B lymphocytes are activated and the role of activated B lymphocytes.
Th cell binds specifically to B lymphocyte; B lymphocyte differentiates into a plasma cell.
Describe how T killer cells destroy a virally infected cell.
Release perforins which punch holes in the membrane of the cell.
Distinguish clearly between an antigen and an antibody.
An antigen is a cell-surface molecule; an antibody is an immunoglobulin manufactured by the plasma cells.
Antibodies are made by plasma cells. Explain how plasma cells are specialised for their role.
Plasma cells have a lot of ribosomes, rough endoplasmic reticulum.
Describe how opsonins function.
Opsonins bind specifically to an antigen on a pathogen.
Describe how agglutinins function.
Agglutinins cross link pathogens by binding specifically.
Describe how antitoxins function.
Neutralise toxin molecules released by a pathogen.
Describe how the structure of an antibody enables it to perform its function.
The variable region is specific to the antigen.
Explain why it may take several days for the primary immune response to become effective.
After infection, the pathogen must be detected and attacked.
Explain why a secondary immune response is so much faster than a primary immune response.
B memory and T memory cells are circulating in the blood.
Give an example of both natural active immunity and natural passive immunity.
Natural active - antibodies made by immune system; natural passive - antibodies provided via placenta.
Explain why passive immunity only provides short-term immunity.
Passive immunity is provided by an external supply of antibodies.
Give an example of artificial active immunity.
Immunity provided by antibodies made in response to vaccination.
Define the term epidemic.
A rapid spread.
What is natural active immunity?
Antibodies made by the immune system in response to infection.
What is natural passive immunity?
Antibodies provided via placenta or breast milk, useful in developing the immune system.
Why does passive immunity only provide short-term immunity?
Passive immunity is provided by an external supply of antibodies, which are proteins that do not last long in the body. They may act as antigens and be attacked by antibodies from our immune system.
Give an example of artificial active immunity.
Immunity provided by antibodies made in response to vaccination (dead/inactive pathogens injected).
Define the term epidemic.
A rapid spread of disease through a high proportion of a population, usually within a country.
How can a microorganism become resistant to an antibiotic?
Bacteria that survive a treatment will be slightly resistant, and the antibiotic acts as a selective force, selecting the resistant individuals. When they reproduce, some of their offspring may be more resistant, thus resistance evolves.
What is a response?
A behavioural or physiological change in an organism as a result of a stimulus.
What is a stimulus?
A change in the internal or external environment of an organism.
What is homeostasis?
Responses that maintain a constant internal environment inside an organism.
Name 4 internal conditions maintained by homeostasis.
Body temperature, blood glucose concentration, blood water potential, carbon dioxide concentration.
Put the aspects of a feedback mechanism in order.
Stimulus, receptor, processor, effector, response.
What are the 2 communication systems in mammals?
Nervous and hormonal.
What is cell signalling?
The release of a chemical from a cell that is complementary to a receptor in a target cell, bringing about a response in the target cell.
What is an effector?
A cell or tissue that brings about a response to a stimulus.
What are the 3 types of effector?
Muscle cells, gland cells, liver cells.
Name 3 types of neurone.
Motor, sensory, and relay.
Describe the structure and function of a motor neurone.
Their cell body is located in the CNS, and they have a long axon carrying the action potential to the effector.
Describe the structure and function of a sensory neurone.
Have a long dendron carrying the action potential from a sensory receptor to the cell body, positioned outside the CNS. They have a short axon carrying the action potential into the CNS.
Describe the structure and function of a relay neurone.
They connect the sensory and motor neurones in the CNS. They have short dendrites and a short axon.
What is meant by a myelinated neurone?
The neurone is insulated by a myelin sheath, which is Schwann cells wrapped tightly around the neurone.
What are the advantages of myelination of neurones?
An action potential can be transmitted much quicker as the signal jumps between the nodes of Ranvier.
Where are non-myelinated neurones found?
They are often used to coordinate body functions such as breathing or digestion, carrying action potentials over shorter distances.
What is a sensory receptor?
A cell or tissue that monitors an aspect of an organism’s internal or external environment.
What do sensory neurones do?
They convert the energy of a stimulus into electrical energy.
Name 6 examples of sensory receptors.
Thermo, chemo, baro, photo, proprio, osmo.
What is a transducer?
Something that converts one form of energy into another.
