The importance of organisms being able to respond to their internal and external environment

Question 1

list points for the importance of organisms being able to respond to their internal and external environment

Answer 1

1. immune response
2. tropism
3. control of heart rate
4. homeostasis

Question 2

immune response: the importance of organisms being able to respond to their internal and external environment

Answer 2

• Animals respond to changes in their internal environment via the immune response where a pathogen is recognised as foreign in the body by a phagocyte, which then engulfs the pathogen via phagocytosis, containing it in a phagocytotic vacuole which fuses with lysosomes to release lysozymes which digest the antigens of the pathogen.
• Phagocytes than active T-cells which bind to the complementary antigen presented by phagocytes to stimulate B cells.
• B-cells bind to the complementary antigen and become activated by clonal selection to divide into plasma cells that secrete antibodies that cause the pathogens to agglutinate together to increase the rate of phagocytosis.
• This response allows animals to destroy invading cells such as viruses, preventing them from replicating and causing cell lysis as well as destroying toxins secreted by bacteria to prevent symptoms such as sickness.
• For example, a failure of the immune system can lead to the invasion of T-cells via the HIV virus which replicates inside of them and causes them to burst, hence there is a decrease of T cells which are available to activate B-cells against other pathogens.
• The progress of the HIV virus can lead to aids, as the organism is unable to trigger an immune system response thus leading to more serious diseases such as tuberculosis.
• Therefore, the importance of an immune system response to an internal environment is the prevention of diseases such as tuberculosis.

Question 3

tropism: the importance of organisms being able to respond to their internal and external environment

Answer 3

• Plants respond to changes in their external environments during the process of phototropism
• The shoots of plants show positive tropism via the diffusion of IAA to the shaded side of the tip, as IAA diffuses down to the shaded side it causes active transport of H+ ions into the cell wall, disrupting the hydrogen bonds between cellulose molecules and the action of expansis makes the cell more permeable to water.
• Cell on the shaded side elongate faster due to higher turgor pressure and the shoots bends towards the light
• This allows the chlorophyll pigment in the leaves to absorb more light to maximise the rate of photosynthesis.
• Without photosynthesis no glucose is produced which is contained in plant cell membranes as cellulose.
• Therefore, the plant cell walls would be unsupported due to lack of cellulose and unable to withstand turgor pressure, turning them flaccid.
• In conclusion, positive phototropism in shoots is important due to the fact that it allows for more light to be absorbed by the leaf for a maximum rate of photosynthesis to synthesise glucose.

Question 4

homeostasis: the importance of organisms being able to respond to their internal and external environment

Answer 4

• Animals respond to a decrease in blood glucose concentration in their internal environment by homeostasis.
• Glucagon is responsible for increasing blood glucose concentration by binding to receptors on the cell membranes and activating enzymes in the liver that break down glycogen stores into glucose via glycogenolysis.
• It also activates enzymes involved in the formation of glucose from glycerol and amino acids via gluconeogensis.
• Lastly, glucagon decreases the rate of respiration of glucose in cells.
• It is crucical that animals maintain a constant blood glucose concentration as glucose is a respiratory substrate that helps to release the energy (ATP) required by respiring cells via aerobic respiration.
• A failure in the response of glucagon can lead to hypoglycaemia which is a symptom of diabetes, it involves fatigue and dizziness.
• In conclusion, it is important that animals respond to changes in blood glucose concentration in order to prevent illnesses such as diabetes.