- Peppered moths show variation in colour - light and dark ones. Before the 1800s there were more light moths than dark moths.
During the 1800s, pollutions have blackened many of the trees that the moths lived on. Dark coloured moths were now better adapted to this environment as they were better camouflaged from predator - therefore would be more likely to survive, reproduce and pas on their dark colouring to their offspring.
Therefore during this time, the number of dark moths increased.
- Taxonomy is the science f classification - involves naming organisms and organizing them into groups based on their similarities and differences, making it easier for scientists to identify and study them.
There are seven levels and groups (called taxonomic groups) used in classification:
Kingdom, Phylum, Class, Order, Family, Genus, Species
Similar organisms are sorted into five Kingdoms and similar organisms from that kingdom would be grouped into phylum. As you move down the hierarchy, the more groups there are but fewer organisms within each group.
This hierarchy ends with a species, a group which contains only one type of organism. A species is a group of similar organisms that are able to reproduce to give fertile offspring. I.e. Lions and tigers can’t produce fertile offspring.
- All species are names using a binomial (two word) system, the first word is the genus name and the second word is the species name. Giving organisms a scientific name enables scientists to communicate in a standard way that minimizes confusion.
* absorbs substances from dead or decaying organisms
** Produces their own food
*** Consumes plants and animal
- Species are classified into taxonomic groups based on many things, i.e. what they look like, their physiology and how related they are. New data must be evaluated by other scientists, if they agree with the new data; it can lead to an organism being reclassified or lead to changes in the classification system structure.
- A new, three domain classification systems have been proposed based on new data which came from molecular phylogeny.
Phylogeny is the study of the evolutionary history of groups of organisms - tells us which species are related to which and how closely related they are.
Molecular phylogeny looks at molecules (DNA and proteins) to see how closely related different organisms are, for example, more closely related organisms have more similar molecules.
- In the older, five kingdom system of classification, all organisms are placed into one of five kingdoms. Whereas the new, three domain system all organisms are placed into one of three domains - large super kingdom that are above the kingdoms in the taxonomic hierarchy.
Organism in the kingdom Prokaryotae (unicellular and without nucleus) are separated into two domain - the Archaea and Bacteria. Whereas organisms from the other four kingdoms (those with a nucleus) are places in a third domain - Eukarya.
The Prokaryotae were reclassified into two domains because molecular phylogeny suggested that Archaea and bacteria are more distantly related than thought.
Plant cell structure and Plant stem
- Cell wall is a rigid structure that surrounds plant cells, it is made mainly of the carbohydrates cellulose, and its function is to support the plant cells.
- Middle lamella is the outermost layer of the cells and it acts as an adhesive, sticking adjacent cells together – giving stability to the plant. It is made of largely of pectin (this sticks cells together and are carbohydrates. There’s n cellulose.
- Plasmodesmatas are channels in the cells that links adjacent cells together this allows for easier transport of substances and communication between cells.
- Pits are regions of the cell wall where the wall is very thin (only primary cell wall is present) They’re arranged in pairs and they allow transport of substance – due to shortened diffusion distance and cell communication.
- Chloroplasts are small flattened structures surrounded by a double membrane with thylakoid membranes inside – which sometimes stacks up to form grana.
Grana are linked together by lamella, which are thin, flat pieces of thylakoid membrane. Some parts of photosynthesis occur in the grana whereas other parts happen in the stroma – a thick fluid found in chloroplasts.
- Amyloplast is a small organelle enclosed by a membrane containing starch granules. Its function is simply the storage of starch granules – they can also convert starch into glucose for release of energy when required.
- Vacuoles are compartments surrounded by a membrane called tonoplast. It contains cell sap, consisting of water, enzyme, minerals and waste products. Vacuoles keep the cells turgid and so prevent the plant from wilting.
They also break down and isolate unwanted chemicals in the cells, also the tonoplast controls what goes in and out of the vacuole.
- The function of xylem vessels is t transport water and mineral ions up the plants form the root to the photosynthetic parts of plants – it also provides support.
As stem ages and the cells in stems stop growing, increasing amount of lignin lays down in the cells walls, making the cell impermeable to water and other substances. The stem becomes stronger, however the cell content dies.
Xylem tissues are long tube like structures formed from dead cells and they have a hollow lumen with no cytoplasm. The end walls on the cells within the tube breaks sown making an uninterrupted tube – allowing water and mineral ions to pass up freely in the centre. They are also coiled to allow for flexibility of stem.
Water and mineral ions moves out of xylem into surrounding cells through unlignified areas / specialised pits. Xylem is found in the centre of the stem.
- Sclerenchyma fibre main role is to provide support to the plant – it is similar to xylem tissue but is fund around the outer edge of stem and in leaves. Like xylem, the Sclerenchyma fibres are dead by maturity.
However they do not have pits or unlignified areas leading t surrounding cells as their main function is purely to provide support, not transport of substances.
Starch, cellulose and Fibres
- Cellulose consists of beta glucose that are alternatively inversed and 1,4 glycosidic bond forms between the molecule through condensation.
These forms straight, unbranched chains of cellulose and each chain are stacked together to from hydrogen bonds between them – forming microfibrils. The strong threads means cellulose provides structural support for cells.
- Plant fibres are made up of long tubes of plant cells, for example Sclerenchyma fibres consist of tubes of dead cells – they’re strong so are useful for rope/fabrics.
- Cell wall contains cellulose microfibrils in a net like arrangement; this structure and the strength of microfibrils make plant fibres very strong.
- Primary cell walls have lots of cellulose, so it provides lots of structural support, and it also contains some pectin. Hemicelluloses are also present which attaches and connects microfibrils. The primary cell wall and middle lamella are present to allow flexibility for cell growth.
Secondary cell wall develops when a cell is older – when it’s done growing. Secondary cell wall contains lots of lignin, which makes it very string. The growth of the secondary cell wall is called secondary thickening.
Plant sustainability and minerals
Sustainability is when we’re using resources in a way that meets the needs of the present generation without destroying the environment/ using up all the resources so the future generations would have none left. (Doesn’t deplete resources)
- Rope and fabrics can be made of plastics (form oil) but are more sustainable if made from plant fibres. Because less fossil fuel is used and crops can be regrown to maintain the supple for future generations.
- Products made from plant fibres are biodegradable, and can break down by microbe. Plants are also easier to grow and process than extracting and processing oil, making them cheaper. However, ropes made from plant fibres are generally not as strong as ropes made of plastic
- Plastic are usually made from oil, some can be made from starch - these are bioplastics. This is similar as vehicle fuel, bioethanol is a fuel made from starch
- Nitrate ions are needed for production of DNA (nucleic acid), proteins and chlorophyll. They are required for plant growth and fruit & seed productions.
Without nitrate ions plants will have stunted growth, and show yellowing - chlorosis.
- Water is needed for photosynthesis, to maintain structural rigidity, transport mineral and regulate the plant’s temperature.
- Magnesium ions are required for the production of chlorophyll - pigment needed for photosynthesis. Lack of this will lead to chlorophyll deficiency (chlorosis).
- Calcium ions (calcium pectate - pectin) fills in gap and links microfibrils, it also provides stability. It is involved in the formation of the middle lamella.
If a plant is deficient in calcium, it may exhibit chlorosis, necrosis (dead areas). Death of meristem tissue (where growth happens - undifferentiated cells) also occurs.
Drug Testing and Drugs from Plants
- Before new drugs become available to the general public they need to be tested, this is to ensure the drug works and don’t have any drastic side effect:
- William Withering was a scientist in the 1700s, he discovered that an extract of foxgloves could be used to treat dropsy (swelling caused by heart failure) and the extract contained the drug digitalises.
- Withering made a chance observation – a dropsy sufferer made a good recovery after being treated with a traditional remedy containing foxglove.
- Although Withering knew the foxglove were poisonous, he started testing different versions of the remedy with different concentration of digitalises – this become known as his digitalis soup
- Too much digitalis poisoned his patients while too little had no effect; it was through this trial and error method that he discovered the correct amount of drug to give to a patient.
- The modern drug testing protocols are much more controlled. Before drugs are tested on any live subjects, computers are used to model the potential effects.
Tests are also carried out on human tissue in a lab before they’re tested on live animals. Then clinical trials are carried out on humans – where new drugs undergo three phases of testing, consisting of more people at each stage:
- Phase 1 involves testing the new drug on healthy individuals, in order to find out things such as safe dosage or side effects & how the body reacts to the drug.
- Phase 2 is carried out if the drug passes phase 1 testing, it will then be tested on a larger group of patients this time and sees how well the drug works in people with the illness / disease.
- Phase 3 is when the drug is compared to existing treatments – which involved testing the drug on hundreds or thousands of patients.
The patients are randomly split into two groups – one group receiving the new treatment whereas the other group would receive the existing treatment. This allows scientists to determine whether the new drug is any better than existing drugs and they can tell at this stage whether the benefits outweighed the risks.
- Results of clinical trials can be made more reliable by using placebo and a double blind study design during the clinical trials:
- In phase 2 clinical trials, the patients are split into two groups. One is given the drug and the other is given a placebo – which is an inactive substance that looks exactly like the drug but doesn’t have any effect.
Here the patient often shows a placebo effect, where they show some improvement as they believe that they’re receiving treatment. Giving half the patients a placebo allows researchers to see if the drug actually works – or if all the patients are just presenting the placebo effect.
- Phase 2 and 3 clinical trials are usually double blind – meaning neither the patients nor the doctors know who’s been given the drug and who’s been given the placebo (or the existing drug)
This reduces bias in the results because the attitudes of the patients and doctors cannot affect the result. I.e. a doctor may think a patient is improving more than they actually have if they know that patient has received the real drug.
- Some plants have antimicrobial properties – they kill or inhibit the growth of microorganisms, this can be investigated by placing plant extracts in bacteria.
Biodiversity and Endemism
- Biodiversity is the variety of living organism in an area, including:
- Species diversity: no of different species & abundances of each in an area.
- Genetic diversity: Variation of alleles within a species.
- Endemism is when a species is unique to a single place (isn’t naturally found in other parts of the world). Conservation is especially importance for endemic species as they’re particularly vulnerable to extinction - since they only live in one place, if their habitat is threatened, they usually won’t be able to migrate and their population number will decline.
- Measuring species biodiversity allows one to compare different habitat and study how a habitat has changed over time:
- One way is to count the no of species in an area - giving the species richness.
- One can also take both the number of species and the number of individuals in the species into account, then work out the species biodiversity using a biodiversity index.
- Estimate of biodiversity in a habitat is based on taking a sample of the population. One needs to choose a small area with the habitat to be sampled. To avoid biased results, this should be chosen at random. If the habitat is a field, it can be divided into a grid and coordinates can be selected using a random number generator.
Than count the number of individuals of each species in the sample area:
- Plants: Quadrant (a frame that is placed on the ground)
- Flying insects: Sweep net (a net on a pole)
- Ground insects: Pitfall trap (a small pit which insects can’t escape)
- Aquatic animals: Net.
- Repeat sampling gives a better indication of the entire habitat. The sample result can be used to estimate the total number of individuals and species richness in the habitat that is being studies. When comparing different habitats, the same sampling techniques must be used.
- Diversity within a species is the variety shown by individual of that species, the individual vary due to having different alleles (different version of the same gene). So genetic diversity is the variety of allele in the gene pool (complete set of alleles) in a species/population.
- The greater the variation of alleles, the greater the genetic diversity. For example, in human, the gene responsible for blood group can have 3 alleles whereas there’s only 1 for gorillas, so human shows greater genetic diversity for blood group than gorilla.
- Phenotype is the observable characteristics of an organism, different alleles codes for different version of the same characteristics. By looking at the different phenotype in a population, you can roughly see the diversity of alleles.
- Genotype is the different sequence of base pairs (different alleles). When analyzed, you can see similarities and differences clearly in the alleles within a species.
Conservation of Biodiversity
- A reduction in global biodiversity can be caused by extinction of a species or the loss of genetic diversity within a species.
- There are currently lots of endangered species; they’re at risk of extinction due to a low population or a threatened habitat. Conservation involves the protection and management of endangered species (i.e. Zoos and sandbanks), they also help to conserve genetic diversity.
- A seedbank stores lots of seed from lots of different species of plants, so if the plant becomes extinct in the wild, the stored seed can be used to grow plants. Seedbanks can help to conserve genetic diversity, they store a range of seeds from plants with different characteristics (and so will have different alleles)
- The work of seedbanks involves:
- Cleaning and drying of seed. (Seeds must be stored at low temperatures)
- Regular testing of seeds to check for viability
- If less than 75% germinate, fresh seeds are collected for storage.
- Seeds are screened suing x-ray, to ensure they contain fully developed embryos.
- Advantages of seedbanks includes:
- Cheaper to store seeds than fully grown plants
- Large number of seed can be stored as they required less space.
- Less labour required to look after seeds than plants
- Seeds can be stored anywhere as long as the conditions are dry and cool, however plants would need the conditions from their original habitat.
- Scientists can study how plants can be successfully grown from seeds, this is useful for when they’re reintroduced back to the wild.
- Can grow endangered plants for use in medical research, as new crops/material. This means endangered plants won’t have to be removed from the wild.
- There are also disadvantages:
- Testing seed for viability regularly can be expensive and time consuming.
- May be difficult to collect seed from plants in remote locations.
- Only studying plants from seeds in a seedbank limits the data to small, interbred populations - info gained may not be representative of wild plants.
- Zoos have captive breeding programmes, which involves breeding animals in a controlled environment.
- The programmes normally breed species that are endangered or are already extinct in the wild. This helps to increase their numbers.
- Some animals can have problems breeding outside their natural habitats, which can be hard to recreate in a zoo. Also, many people think it is cruel to keep them in captivity.
- Reintroducing plants grown from seedbank or animals bred in zoos can increase their numbers in the world. This helps to conserve their numbers or bring them back from the brink of extinction.
- This could also help organisms that rely on these endanger plants/animal as food, or as part of their habitat. This reintroduction can also contribute to restoring habitats that have been lost, for example. Rainforests that have been cut down..
- Reintroduced organisms could bring new diseases to habitats - harming other organisms that live there. Also, they may not behave as they would if they’d been raised in the wild. I.e. Problems finding food or communication with wild members of their own species.
- Research in zoos increases knowledge about the behaviour physiology and nutritional needs of animals - contributing to conservation efforts in the wild. Zoos can also carry out research that’s not possible for some species in the wild, i.e. Nutritional or reproductive studies. However, animals in captivity may act differently to animals in the wild.