biology topic 5

• Photosynthesis is a reaction in which light energy is used to split apart the strong bonds in water molecules, in a process of photolysis, in order to combine hydrogen with carbon dioxide to produce a fuel in the form of glucose.
• Oxygen is a waste product of photosynthesis and is released into the atmosphere.
• The rate of photosynthesis is determined by carbon dioxide concentration, light intensity as well as temperature.
• Chloroplasts are the site of photosynthesis and this organelle is adapted to photosynthesis in the following ways: it contains stacks of thylakoid membranes called grana which contain the photosynthetic pigments, such as chlorophyll, arranged as photosystems and it contains stroma which is the fluid surrounding the grana, stroma contains all the enzymes required for the light independent stage of photosynthesis.
• Photosynthetic pigments are involved in absorbing light required for photosynthesis and subsequently convert it to chemical energy.
• The colour of pigments is determined by the light they reflect.
• Chlorophylls absorb red as well as blue-violet light, they only reflect green light, thus giving chlorophyll green colour.
• The two forms of chlorophyll are chlorophyll a with the highest abundance which absorbs light at 430 nm and 663 nm, and chlorophyll b, which absorbs at 453 nm and 642 nm.
• Apart from chlorophyll, carotenoids are also involved in photosynthesis and serve to prevent damage of chlorophyll.
• Carotenoids are present in two forms, beta carotene which is orange in colour and xanthophyll which is yellow in colour.
• An absorption spectrum can be used to determine the wavelengths absorbed by particular pigments by illustrating the percentage of light absorbed at a particular wavelength.
• An action spectrum illustrates the relationship between the rate of photosynthesis for a given wavelength.
• Chloroplast photosynthetic pigments can be separated in a process called chromatography.
• The process of chromatography requires building up a concentrated spot of pigments on a chromatography plate and immersing the plate in a solvent, which travels up it, separating the different pigments as they have differing solubilities in the solvent.
• The stages of photosynthesis occur in two stages, the light-dependent reaction and the light-independent reaction (also known as the Calvin cycle).
• Eventually , a climax community is established which is the final stage of succession, a self-sustaining and stable community of organisms.
• Pollen in peat bogs can give us an idea of what kind of plants were present at the time when the peat was being formed.
• Increasing levels of carbon dioxide in the atmosphere are believed to contribute towards climate change as carbon dioxide is a greenhouse gas and is involved in the greenhouse effect.
• Succession: The change of one community of organisms into the other.
• Secondary succession occurs in a previously colonised area in which an existing community has been cleared.
• Global warming is a term used to describe a gradual increase in the average temperature of the Earth’s atmosphere and surface.
• Anthropogenic climate change is climate change caused by human activity such as burning fossil fuels leading to the release of greenhouse gases.
• The area is first colonised by the pioneer species, such as lichens, which are adapted to survive in such harsh conditions.
• Distribution of organisms in a habitat is affected by its niche and abiotic and biotic factors as they determine how easy it is for an organism to survive and thrive in a location.
• Global warming is believed to lead to a permanent change in the Earth’s climate.
• Ecosystem: A relatively self-contained unit consisting of all the organisms living in a place including the abiotic and biotic factors.
• Habitats with low levels of competition and high availability of nutrients, water and space will have large populations of organisms.
• Another human cause of climate change is the destruction of forests for land to be used for things like building and agriculture.
• Dendrochronology is the study of tree rings as the size of tree rings is affected by temperature.
• Niche: An organism’s role in the ecosystem, including the abiotic and biotic factors required for its survival.
• Primary succession occurs when area previously devoid of life is colonised by communities of organisms, for instance after the eruption of a volcano which lead to formation of a rock surface.
• Over time, the soil becomes richer in minerals, enabling larger plants such as shrubs to survive.
• As organisms die, they add and are decomposed by microorganisms, thus adding humus, this in turn leads to formation of soil which makes the environment less hostile, more suitable for more complex organisms.
• Temperature records enable analysis of changes in temperature.
• The data from scientific studies can be extrapolated to make predictions which can then be used in models of future climate change.
• The light-dependent reaction occurs across the thylakoid membrane, the ATP and reduced NADP produced then take part in the light-independent reaction in the stroma.
• Evolution occurs as a result of change in allele frequency which in turn is affected by changing selection pressures.
• Sympatric speciation is where new species evolve from a single ancestral species when inhabiting the same geographic region, so reproductive isolation occurs without the population being physically separated.
• Denaturing of enzymes can stop many important biological reactions occurring, potentially leading to the deaths of animals, plants and microorganisms.
• A change in environment leads to a change in selection pressures which in turn makes some alleles more desirable than others.