The structure of a dicotyledonous root in relation to the pathway of water from root hairs through the cortex and endodermis to the xylem. Apoplastic and symplastic pathways. Transpiration and the effects of light, temperature, humidity and air movement. The roles of root pressure and cohesion-tension in moving water through the xylem.

The structure of a dicotyledonous root in terms of the up take of water.

The first cell is a root hair cell. This is an epidermal cell with a long extention which provides a large surface area for the diffusion of water.

There is a high water potential in the soil, because there are not many ions dissolved in it, and there is a low water potential in the cell, because the vacuole contains cell sap which has many ions dissolved in it, water moves by osmosis from the soil into the root hair cell.

The second cell is a parenchyma (packing) cell of the cortex, water moves between these cells in two ways.

1. The symplastic pathway- cell walls have spaces in which water can move along
2. The apoplastic pathway- there are strands of cytoplasm called plasmodesma which link the cytoplasm of different cells, water moves through these along the concentration gradient by osmosis.

The third cell is an endodermal cell. Water in the apoplastic pathway arrives in the ‘protoplast’ of the cell through the plamodesma, but water in the symplastic pathway has to be forced out of the cell wall by a waterproof strip called the Casparian strip.

Root pressure

Endodermal cells actively transport ions into the xylem, this means the xylem has loads of ions in it and so has a really low water potential- so water will move into the xylem as there is a concentration gradient. This helps move water through the plant and is known as ‘root pressure’.

Water moved through a leaf

Water moves from the roots to the leaves through the xylem. When it reaches the leaf it is moved into the mysophyll cells through the apoplastic and symplastic pathways. Water evaporates from the mysophyll cells into the air spaces in the leaf, it then leaves through the stomata- this is called transpiration.

Cohesion-tension theory

Water molecules stick together due to hydrogen bonds formed between them, this is called ‘cohesion’. When water molecules are moved through the leaf they pull other molecules up behind them- this means that as water molecules evaporate from the mysophyll they pull more molecules into the cell behind them, in turn this pulls molecules up in the xylem. In this way there is a pull on the water in the xylem which moves water in the stem.

Factors affecting transpiration

Temperature:

this evaporates more water (by increasing kinetic energy and so the space between molecules making them a gas.) It also decreases the humidity of the air.

Humidity:

humid air has many water molecules in and so it has a low water potential- this means less water can diffuse into it.

Air movement (wind speed):

the more air movement, the more quickly water vapour gets taken away from the stomata- this means that the air can be cleared of vapour and have a higher water potential and more water will diffuse out of the leaf into it.

Light:

photosynthesis happens when there is light, so the more light, the more photosynthesis, the more gas exchange is needed to happen. This means that when it is light the stomata will open and therefore water vapour will escape.

An index of diversity describes the relationship between the number of species and the number of individuals in a community. Calculation of an index of diversity from the formula. Candidates should be able to • calculate the index of diversity from suitable data • interpret data relating to the effects of human activity on species diversity and be able to evaluate associated benefits and risks • discuss the ways in which society uses science to inform the making of decisions relating to biodiversity.

The index of diversity is a way of quantifying species diversity.

The formula is as follows (this will be given in an exam):

sciencebitz

where N= total number of organisms of all species (community)
and n= total number of organisms of each species

This means that, if we take a quadrant from a rain forest and we see one tree, five birds, twenty ants and two snakes the equation will be as follows:

1+5+20+2(1+5+20+2-1)                  
(1(1-1))+(5(5-1))+(20(20-1)+(2(2-1)
=
28(27)                          
1(0)+5(4)+20(19)+2(1)
=
756               
0+20+380+2
=
756
402
=
1.9

Courtship behaviour as a necessary precursor to successful mating. The role of courtship in species recognition.

Species all display different behaviour, this helps them to recognise each other.

This is beneficial to a species as they want to breed with each other so that they produce fertile offspring and pass on their genes.

There are other advantages of specific behaviour displayed during courtship:

• Show that they are capable of breeding: to optimise the chance of producing offspring.
• Form a pair bond: to successfully raise the offspring.
• Mate at an appropriate time: optimise the chance of fertilisation.

The principles and importance of taxonomy. Classification systems consist of a hierarchy in which groups are contained within larger composite groups and there is no overlap. The phylogenetic groups are based on patterns of evolutionary history. A species may be defined in terms of observable similarities and the ability to produce fertile offspring. One hierarchy comprises Kingdom, Phylum, Class, Order, Family, Genus, Species. Candidates should be able to appreciate the difficulties of defining species and the tentative nature of classifying organisms as distinct species.

Taxonomy is the system used to group organisms, it is important to scientist to establish the relationships between different species.

All organisms originated from the same organism but through evolution have ended up with significant amounts of variation.

Phylogenetic groups are how recently two species have been related (how recently they evolved apart into different species).

Sometimes organisms are organised due to observable physical characteristics which do not necessarily mean they are closely genetically related.

Classification is not yet perfected due to the sheer number and the complexity of life on earth.

The most common system is:

scunderwood

The definition of a species is a group of organisms which can breed to create fertile offspring.

https://www.youtube.com/watch?v=F38BmgPcZ_I

The cells of multicellular organisms may differentiate and become adapted for specific functions. Tissues as aggregations of similar cells, and organs as aggregations of tissues performing specific physiological functions. Organs are organised into systems.

Each cell in the body starts off the same but then they specialise by expressing certain genes.

This is beneficial as different cells are better off at carrying out certain jobs.

Aggregation is grouping together.

A groups of similar cells function together as a tissue (are aggregated).

Tissues are then aggregated into organs. These have several different types of tissue which function together as a system.

Similarities and differences between individuals within a species may be the result of genetic factors, differences in environmental factors, or a combination of both. Candidates should appreciate the tentative nature of any conclusions that can be drawn relating to the causes of variation.

Both genetics and environment can have an effect on the things that make up an individual. Key examples include genes on eye colour, environment on how far you reach your growth potential and environment and genes on skin colour.

It is often difficult to tell weather variation is environmental or genetic. In almost all cases it is a mixture of both. The prime display of this being that two twins with exactly the same genes have the potential to end up very different.

There are three things that cause genetic variation:

• The random fusion of gametes: the specific sperm and egg that happened to meet at the specific moment that a offspring is created are completely random and have a massive effect on the genes inherited.
• Mutations: DNA can be changed by mistakes in copying or caused by things like radiation.
• Meiosis: this form of cell division that creates gametes has crossing over (genetic recombination) and independent segregation which both vary the genes inherited.

The concept of normal distribution about a mean. Understanding mean and standard deviation as measures of variation within a sample. Candidates will not be required to calculate standard deviation in questions on written papers. Candidates should be able to analyse and interpret data relating to interspecific and intraspecific variation.

When figures get larger towards the mean with no bias left or right, the graph will have this shape:

Mathsisfun

The shape is known as a bell curve and the distribution of values is called 'normal distribution'.
If a graph has normal distribution, then 68% of the results will be within 1 standard deviation and 95% of results will be within 2 standard deviations:

Biologyforlife

Standard deviations are a measure of accurate data is; the scattering of data around the mean.

The more centrally (around the mean) scattered they are then the more accurate the data is. If data is really spread out and there is only a small proportion of the data that is near the mean then it will have a large standard deviation, and will not be good data to draw conclusions from.

To work out standard deviation you add together all the deviations and then divide this by the number of values minus one.

To work out a deviation, first find the mean then subtract the it from a value. This answer needs to be squared to eliminate negative numbers. Do this for each value and then add them up. Divide this number by the number of values minus one. Find the square root.

You don't actually need to be able to do this according to the mark scheme, but it would seem wise to learn it.

For example, if I have 1, 2 and 3 and I want to work out the standard deviation I first find the mean
This is done by adding up all the values and dividing by the number of values you have (3):
1+2+3= 6
6/3=2
Next you need to subtract the mean from each value and square the answer:
1-2= -1
-1 squared= 1
2-2= 0
0 squared= 0
3-2= 1
1 squared= 1
Then add together all these answers:
1+0+1= 2
Now divide this by the number of values (3) minus one:
2/2= 0
Now find the square root of this:
the square root of 0= 0
So here one standard deviation is zero.

https://www.youtube.com/watch?v=hUaua15QzK4
https://www.youtube.com/watch?v=gV1gUdFvI54

Variation exists between members of a species. The need for random sampling, and the importance of chance in contributing to differences between samples.

Members of a species differ from each other (intra-specific variation).

We can use random sampling to analyse these differences.

This involves taking a small number of individuals at random from a population, analysing them, gaining statistics and then making the assumption that these statistics are the same for the whole population.

Normally this is carried out by having a grid of an area and using a random number generator to pick squares in the grid to analyse.

The benefit of random sampling is that there are multiple values put in so you get an average, reducing anomalies and making the result more representative, however because the figure is taken from just a sample, it means that you do not have to attempt to find a figure for every single individual.

Unfortunately there is an element of chance involved meaning that the statistics gained may be inaccurate as a non-representative sample was chosen. However, by increasing the sample size you can decrease the element of chance.

DNA is the genetic material in bacteria as well as in most other organisms. Mutations are changes in DNA and result in different characteristics. Mutations in bacteria may result in resistance to antibiotics. Resistance to antibiotics may be passed to subsequent generations by vertical gene transmission. Resistance may also be passed from one species to another when DNA is transferred during conjugation. This is horizontal gene transmission. Antibiotic resistance in terms of the difficulty of treating tuberculosis and MRSA.Candidates should be able to • apply the concepts of adaptation and selection to other examples • evaluate methodology, evidence and data relating to antibiotic resistance • discuss ethical issues associated with the use of antibiotics • discuss the ways in which society uses scientific knowledge relating to antibiotic resistance to inform decision-making.

Bacteria carry DNA both as circular chromosome and as plasmids (little rings of DNA).

Mutations are random changes that occur to the DNA sequence. A change in DNA results in different protein being produced, this changes the characteristics of an organism.

Variation is caused by two things: mutations; recombination of existing DNA.

Conjugation
Bacteria do not sexually reproduce, so until recently it was unknown how bacteria were so diverse without recombination of existing DNA, however, now we know that there is recombination of existing DNA but not from two parents to an offspring, it happens from one existing bacteria to another: plasmids are transferred between them in a process known as conjugation:

• One bacteria starts to grow a tube called a pilus or conjugation tube
• It also starts to replicate a plasmid
• The tube reaches another bacteria and the DNA starts to move through it as a line
• It enters the new bacteria and forms a ring (the new plasmid)
• The tube is broken down

This process takes a matter of seconds and allows the transfer of genetic material from one existing bacteria to another- this is known as horizontal gene transmission (because it occurs across a generation). In this way a mutation could be passed between the same type of bacteria, to a different strain, or even to a different species. Like this resistance to an antibiotic could be gained by a species.

Bacteria also pass DNA on by asexual reproduction, this is known as vertical gene transmission as DNA is passed down from one generation to another.

Conjugation discovery

In 1946 Lederberg and Tatum designed an experiment to prove that DNA was transferred horizontally between bacteria:

• Take two strains of E. coli, one that can synthesise everything but methionine and biotin and one that could synthesise everything but threonine and leucine
• This meant that when they were placed in a medium without the nutrients neither strain could grow
• They mixed the two together and left them for several hours
• They put the mixture back onto a medium with no nutrients
• Some bacteria were able to survive
• This meant that there must have been DNA exchanged so that the strains had the ability to synthesise the nutrients they needed to survive

Antibiotic resistance

Most of the time mutations are not beneficial to an organism, they stop it from being able to function properly, however, occasionally a mutation happens that can increase the success of an organism.

In bacteria mutations can occur that make them resistant to antibiotics, this means that if they are in an infected person who is taking antibiotics then all the other, non mutated bacteria will die off, the one with the mutation will survive and replicate passing on the resistant gene and making the resistant bacteria more common.

This will only occur because of the presence of antibiotics giving the resistant strains an advantage, therefore the more antibiotics are used, the more resistance happens.

An example of this is the mutation of an enzyme in a bacteria that changed an enzyme to make one which could break down penicillin (an antibiotic) before it could harm the bacteria. This meant that it was not destroyed by the antibiotic and lived on to reproduce successfully. The gene was then passed on to future generations of the bacteria to make a resistant population, but it was also transferred horizontally so that other species were also resistant.

Discovering resistance

A bacteria is placed in a Petri dish with an antibiotic. If the bacteria is not resistant then it will not be able to grow near the antibiotic, and it will be visible everywhere apart from near the antibiotic. It the bacteria is resistant it will grow even in the area of the antibiotic and therefore will be visible over the whole dish.

Tuberculosis

To treat the bacterial infection of tuberculosis (TB) you have to take a 6-9 month course of antibiotics. Often people start to feel better a little way into the course because a lot of bacteria has been killed off so they stop taking the antibiotic. However, even though a lot of bacteria had been killed off, some would not yet have died- this is the more resistant stuff that is harder to kill. As a consequence the resistant bacteria are left in the body, free to multiply and spread. This is known as selection pressure.

As a result, TB is resistant to most known antibiotics- the definition of a super bug.

MRSA

Methicillin-resistant staphylococcus aureus (MRSA) is also a super bug. It is found in hospitals where: people tend to be ill anyway, making them more susceptible to infection; people are in close proximity; there is a lot of contact (doctors patients); there are a lot of antibiotics being taken (which make resistant strains more successful.

Antibiotics may be used to treat bacterial disease. One way in which antibiotics function is by preventing the formation of bacterial cell walls, resulting in osmotic lysis.

Bacteria in the body may cause disease, this can be treated by the use of antibiotics.

These work in a variety of ways to kill off bacteria. One way in which this can be one to cause osmotic lysis:

• Antibiotics can prevent the formation of the proteins for peptide cross linkages in cell walls
• This means that the cell wall which regulates water movement cannot be formed
• As a result, water moves by osmosis into the cell
• Eventually the cell will become too full and burst, this is called osmotic lysis

Diversity may relate to the number of species present in a community. The influence of deforestation and the impact of agriculture on species diversity

Community- all the different species living in an area.

Diversity is the variation in species living in an area: it is important to look at the amount of different species but it is also important to look at the size of each of the species.

This is because there could be many species, but some could be very unsuccessful or endangered and others could be successful and dominant.

An example of where this is important is in an agricultural setting where a certain crop is cultivated. For example in a wheat field, there will be some insects and mammals so potentially lots of species, but they will all have a relatively small number of members compared to the wheat which will have a huge number of individuals. Here, even though there are many species the biodiversity is low.

Deforestation causes disruption to the relationships in a community by removing on species (trees) and decreasing the biodiversity. Important things such as food and habitat are lost which can cause a decrease in the population of other species.

The structure of arteries, arterioles and veins in relation to their function. The structure of capillaries and their importance in metabolic exchange. The formation of tissue fluid and its return to the circulatory system.

All the blood vessels have a lining or endothelial layer which prevents friction.

Arteries

• Carry blood away from the heart
• Blood inside is high pressure to push blood all the way round the body
• Thick muscle layer so the amount of blood going through can be controlled
• Thick elastic lining to maintain pressure
• Having thick walls also helps prevent it from bursting
• Small lumen keeps the pressure high

Arterioles

• Are in between arteries and veins to decrease the pressure before the blood reaches the capillaries so they don't burst
• Thick muscle layer so that it can control the blood flow into the capillaries
• Thinner elastic layer as pressure is not so high

Veins

• Carry blood back to the heart
• Doesn't need a thick elastic layer because the blood pressure is low (no danger of bursting)
• Thin elastic and muscle layers make it easy to compress so that blood can be pushed through
• Valves make sure blood doesn't flow in the wrong direction

Capillaries

• Thin lining layer and no muscle or elastic layer so there is a small diffusion distance
• It is also small so that it can get in between tissues so cells are close, decreasing the diffusion distance again
• Spaces in lining to let white blood cells through
• There are lots of them and they are small to increase the surface area

Large surface area and small diffusion distance are key to aiding fast diffusion, this is key because it is through the capillaries that crucial metabolic substances like oxygen are delivered to the cells of the body

stevegallik

Tissue fluid
At the arteriole end of capillaries there is a lot of blood pressure (hydrostatic pressure), this forces substances out by pressure filtration. Water and some other substances are pushed out of the capillaries into what is know as the tissue fluid (however large molecules like proteins cannot fit through the gaps); this surrounds cells and delivers substances to them like glucose, amino acids and oxygen.

Because a lot of water moved out of the capillary but the proteins remained, at the venous ends of the capillary, the water potential is very low: this causes water in the tissue fluid move back into the blood by osmosis. Some of the liquid enters the lymphatic system, but most then renters the blood at the neck.

Similarities and differences between organisms may be defined in terms of variation in DNA. Differences in DNA lead to genetic diversity. The influence of the following on genetic diversity • selection for high-yielding breeds of domesticated animals and strains of plants • the founder effect • genetic bottlenecks. Candidates should be able to discuss ethical issues involved in the selection of domesticated animals.

Genetic diversity is the level of variation between organisms, the more differences in DNA (nucleotides, genes of genomes) the larger genetic diversity. It can also be defined as the number of different allels present in a population.

Genetic variation is seen as a good thing because it reduces the inheritance of genetic diseases from recessive alleles. It also means that if a disaster occurred (e.g. a change of atmosphere or the introduction of a new predator) some of the species may be able to survive because of their differences.

Selective breeding
This is where humans choose animals or plants with desired characteristics and breed and nurture them. The selected ones will be more successful at reproducing as they are encouraged by the humans and therefore be a successful species.

A prime example is the breeding of dogs, which was occurring even in the Roman times when wolves with the ability to read human behaviour were selected to breed and keep as pets.

Another species that this can be seen in is the pig, where wild boar were captured and farmed. Characteristics such as being fat (more food) and having small legs (can't run away) meant the animals would be selected to have offspring to pass on the traits. Years of selective breeding have left us with the domestic pig, too fat and disproportionate to walk properly- it raises ethical issues about weather it is fair to manipulate the DNA of animals for domestic qualities as it does not benefit a species and can reduce their chances of survival in the wild.

The founder effect
When some of a population moves to start a new colony, only some of the alleles will be taken. This means that in the new community there a smaller variety of different DNA so genetic diversity is decreased. This can cause problems, for example in the Amish community, people suffer from many genetic disorders because they are more likely to have two parents with the same genotype who are both carriers.

Bottle necks
A similar thing can happen when the size of a population suddenly drops- some alleles may be completely lost (either by chance or because their characteristic was vulnerable), decreasing the genetic diversity. When cheetahs died in the ice age, the population sank to around just fifty, of the survivors a very high proportion had fertility issues, this meant the characteristic was passed on to a high proportion of the offspring and that even as the population began to expand again the percentage with fertility issues remained high.

Comparisons of amino acid sequences in specific proteins can be used to elucidate relationships between organisms. Immunological comparisons may be used to compare variations in specific proteins. Candidates should be able to interpret data relating to similarities and differences in base sequences in DNA and in amino acid sequences in proteins to suggest relationships between different organisms.

Genes code for amino acids to make proteins. So if we look at a protein in two different species and examine its amino acids, we can see how similar or different their genes are.

For example, (arbitrary data used) if we took heamaglobin from a gorilla and a human and looked at the amino acids and they looked like this:
Human: Ser; Val; Ser; Glu; Ile; Gln; Leu; Met; His; Asn
Gorilla: Ser; Val; Val; Ser; Ile; Gln Leu; Met; His; Asn
then we could see they are relatively genetically similar with  7/10 amino acids are the same.

One way to compare proteins is by comparing antigens on the body cells of a specie. This is immunological comparison:

• Extract blood serum from a species
• Put it in a second species
• This species will produce antibodies that are complimentary to the antigens of the first species
• Extract the antibodies
• Mix them with the blood serum of a third species
• A precipitate will form if the antibodies respond to the antigens of that specie

If the antibodies that were created for the antigens of the first specie can respond to antigens of the third then that means it must be complimentary to both. That means that both antigens had a similar tertiary structure, which means they had a similar primary structure, which means they had a similar sequence of amino acids which means that had a similar base sequence which means they are genetically similar. Therefore antibody can respond to both= more precipitate= more genetically similar.

If there is not very much precipitate its because the antibody can respond to the antigens in the third species because it is not sufficiently similar to the first, this shows us that they are genetically dissimilar.

Comparison of DNA base sequences is used to elucidate relationships between organisms. These comparisons have led to new classification systems in plants. Similarities in DNA may be determined by DNA hybridisation.

If two species have recently shared a common ancestor, then they are closely related. If this is the case, then they will have much of the same DNA because when one species gives rise to another they initially have similar DNA.

Over time mutations will render the DNA very different through the accumulation of mutations. This means that species that have not shared a common ancestor recently will have very different DNA.

So by looking at DNA scientists can determine what other species a species is related to and therefore what type it should be classified as.

A recent example of where this has been useful is in the classification of plants. Before genetic comparison plants had been categorised due to physical characteristics, however when the DNA was examined, scientists found that some plants that looked very different had more similar genes than ones that looked similar. The whole plant kingdom had to be re-classified.

DNA hybridisation is one method of comparing the base sequence of DNA:

• Heat the DNA of two species, this will break the hydrogen bonds holding together the two sides of the chromosome
• Leave them to cool and reform hydrogen bonds between complimentary base pairs
• Some of the DNA will have formed with one strand from each species
• This 'hybrid' DNA is then heated in stages to see at what temperature it separates into single strands

A higher temperature means more energy was required because there are more hydrogen bonds, this means that there were many complimentary base pairs made, and that means that the DNA from both species was similar.

If the DNA was not similar there would not be very many complimentary base pairs, so the hybrid DNA would have few hydrogen bonds and not take very much energy to break them all. This means that hybrids strands that separate at a low temperature come from two species that are not genetically similar.

Genetic comparisons can be made between different species by direct examination of their DNA or of the proteins encoded by this DNA.

Genetic comparisons are made to find out the classification of a living thing, i.e. what its ancestors are.

Comparing DNA will show what characteristics two species have in common, and what mutations have been made to make them different.

This can also be done by looking at proteins because DNA codes for amino acids which make up proteins. Therefore looking at one protein from two species and seeing the similarities and differences in amino acids equates to seeing similarities and differences in their genetics.

The basic structure and functions of starch, glycogen and cellulose and the relationship of structure to function of these substances in animals and plants.

Starch is the form of carbohydrate which plants store energy as: in small grains especially in the seeds and storage organs.
It is a polysaccharide made up of α-glucose to make a long straight chain which then winds up tight (unbranched helical chain).
Being wound up so tight means you can fit a lot of it in a small space and therefore a convenient way to store energy.
It is also a positive that it is made up of α-glucose, because this means when it is hydrolysed (broken down) that will be the molecule produced and it is easy to transport and use in respiration reactions.
Starch is also insoluble, this is good for two reasons: one, it does not tend to diffuse out of cells; two, it doesn't tend to draw water into cells by osmosis.

Glycogen is the form of carbohydrate which animals store energy as: in small granules especially in the muscles and liver.
It is a polysaccharide made up of α-glucose to make a short and very branched chain which winds up tight (branched helical chain).
Like starch it is insoluble, fits a lot of energy into a small space and makes α-glucose when hydrolysed, but because it is shorter is is hydrolysed more quickly.

Cellulose is found in plant cell walls.
It is a polysaccharide made up of β-glucose. If you have two β-glucose molecules and perform a condensation reaction, one of the molecules will have to turn up side down; this is because the order of the OH and the H is reversed on one side, so to match up it has to be turned round. This fact means that in a chain of β-glucose the 'CH2OH' group will alternate between being at the top and the bottom of the chain. The importance of this is that it can't coil up.
So, the chain is straight and unbranched which means several chains can lie next to each other; hydrogen bonds will form between these chains creating a strong 'microfibril' (what fibres are made of).

Beta glucose forming a glycosidic bond

Chain of cellulose

nutrition.jbpub

The structure of b-glucose as... b-glucose and the linking of b-glucose by glycosidic bonds formed by condensation to form cellulose.

β-glucose has the same chemical formula as α-glucose, and the other hexose sugars (C6H12O6), but a different structure:

In a condensation reaction, the following will be formed:

Water is formed from the OH of the one glucose and the H of the others OH, the left over O forms a glycosidic (between sugars) bond.

Many β-glucose joined together in this way a polysaccharide called cellulose will be formed. 

There are fundamental differences between plant cells and animal cells. The structure of a palisade cell from a leaf as seen with an optical microscope. The appearance, ultrastructure and function of • cell wall • chloroplasts. Candidates should be able to apply their knowledge of these and other eukaryotic features in explaining adaptations of other plant cells.

Plant cells and animal cells share some of the same organelles, but there are some that differ. Cell walls and chloroplasts are examples of things that plant cells have which animal cells don't. Bother can have vacuoles but plants almost always have large central ones and animals rarely have them, and when they do they are small and scattered. Another difference is that plants store glucose as starch and animals store it as glycogen.

A palisade cell is traps sunlight with chlorophyll, it is found in the leaf.

cell-specialisation-jesse.wikispaces

Cell wall
This is needed in a plant cell to offer structural support, stop cells bursting and provide the symplastic pathway for water movement. They are made up of polysaccharides, like cellulose, and have a middle lamella which holds adjacent cells together.

sigmaaldrich

Chloroplasts
These are needed in plant cells as they need the suns energy to carry out photosynthesis.
They are made up of three parts:

• The chloroplast envelope- double plasma membrane to control the movement of substances in and out of the cell.
• The grana- stacks of disks (thylakoids) which contain chlorophyll and have a large surface area for the first stage of photosynthesis. Tubular extensions can link them.
• The stoma- matrix with the enzymes needed for the second stage of photosynthesis
• DNA and ribosomes to manufacture proteins for photosynthesis

artinaid

Root hair cells adaptations

• Carrier proteins for active transport
• Lots of mitochondria to produce ATP for active transport
• Long thin shape to increase surface area for diffusion
• Large vacuole containing a high proportion of ions to decrease the water potential and encourage osmosis into the cell

Xylem vessel adaptations

• Thick walls to cope with the negative pressure of transpiration
• Thickening happens in a spiral so the plant is still flexible
• They are hollow and elongated so that water can move up them
• They are dead so that water does not need to diffuse through anything and can go quickly through
• Have a substance called lignin in their walls to offer strength and make it water proof (so water doesn't move out by osmosis)

The general pattern of blood circulation in a mammal. Names are required only of the coronary arteries and of blood vessels entering and leaving the heart, liver and kidneys.

Mammals have a double circulatory system, this means that there are two different sides of the heart pumping to two different places (the lungs and the rest of the body.)

We need a system like this because mammals are so large and so things need to be transported long distances and we are have a fairly high metabolic rate so we need a lot of oxygen transported.

Heart
The vein that brings blood into the heart from the body is called the vena cava.
The artery that takes blood out of the heart and to the lungs is the pulmonary artery.
The vein that brings blood into the heart from the lungs is the pulmonary vein.
The artery that takes blood out of the heart is called the aorta.

Liver
The hepatic artery brings blood in.
The hepatic vein takes blood out.
The vein that brings blood to the liver from the stomach is the hepatic portal vein.

Kidneys
The renal artery brings blood in.
The renal vein takes blood out.