1. Memory cells that trigger a secondary immune response
2. Specific antibodies that remain concentrated in the bloodstream for life after the first infection event
3. Memory cells that trigger a primary immune response
4. T cells that trigger a primary immune response
Answer:
1. Memory cells that trigger a secondary immune response
Explanation:
During the first infection when the body is invaded by a particular antigen, the immune system tries to identify the type of antigen. B lymphocytes make antibodies when the antigen has been identified in the event of a primary infection. The response of the immune system during the primary infection of that pathogen is usually slow. As soon as the primary infection is arrested by the antibodies produced in response, memory cells such as the memory B cells is formed, which enables the immune system to identify the same pathogen, and thereby triggers a faster secondary immune response in subsequent infections by the same pathogen.
The correct answer is option B
Species interactions are categorized based on their reciprocal effects (the effects that the interaction has on each species/individual involved).
1. Bees pollinate plants as they move from flower to flower collecting pollen.
This is a mutualistic relationship because the both species involved in this interaction benefit from the interaction. The bee benefits because it obtains nectar which is provided by the plant. The plant benefits because the bee carries the plants pollen to other plants, allowing the plant to reproduce.
2. Green algae grow on the backs of spider crabs living in shallow water.
This is another example of a mutualistic relationship because both species involved in this interaction benefit from the interaction. The spider crab benefits from the camouflage that the algal growth provides, while the algae benefits from the protection from predators provided by the spider crab.
3. Fleas living on skin of dogs and obtaining nutrients from dogs blood.
This is a parasitic relationship because one of the species benefits from the interaction while the other species in negatively impacted by the interaction. The flea benefits from the nutrients obtained from the dogs blood while the dog is negatively impacted by the fleas presence (loss of blood, discomfort).
4. Nitrogen-fixing bacteria obtain nutrients from host plants and use the nitrogen to supply host plants with nitrogen.
This is an example of mutualism because both species in this interaction are benefitting from the interaction. The nitrogen fixing bacteria benefit by receiving nutrients from the host plant while the host plant is benefitting from receiving nitrogen from the bacteria.
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In cell signalling, after a signal is sent, signal molecules bind to receptors on target cells and some activity in a target cell changes.
There are three stages in cell signalling :
1. The process of reception occurs when a signalling molecule from the extracellular environment is recognized by a cell. The chemical signal, which is also known as a ligand, is recognized as a signal when it attaches to a receptor protein either on the exterior of the cell or on the interior of the cell.
2. Transduction: This process occurs when the signalling molecule interacts with the receptor, which causes a change in the protein that makes up the receptor. The process of transduction is kicked off by this modification. In most cases, signal transduction occurs through a pathway that consists of numerous stages. The signal transduction route contains relay molecules, each of which influences the subsequent molecule in the pathway.
3. Reaction: In the third and last step, the signal causes a certain cellular response.
Learn more about cell signalling here :
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They can cause changes in a certain cell that can cause the growth or death in a cell.
