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The maintenance of constant conditions in the body


What needs to be kept constant in the body and why?

Oxygen levels, pH and temperature (for enzymes), salt/ion content (osmotic balance)


Basic features of homeostatic system

1. A control system with sensors/receptors
2. A corrective mechanism
3. A negative feedback system to prevent over correction


How is body temperature regulated?

1. Glands in hypothalamus/heat receptors in the sin detect changes in temperature
2. Sweat glands are stimulated to release sweat and/or vasodilation occurs
3. Blood temp is constantly monitored and as it returns to set point the degree of vasodilation/amount of sweat produced decreases to prevent over correction


Homeostatic mechanisms in the kidney

Excretion: the removal of the toxic waste products of metabolism
Osmoregulation: the maintenance of optimal water potential of body fluids


What does the kidney excrete?

Urea (a nitrogenous waste product formed in the breakdown of amino acids in the liver) and creatinine (produced from the breakdown of creatine phosphate, a molecule important in ATP synthesis in muscles)


Blood flow through kidney

Blood flows from aorta into the renal artery at high pressures needed for filtration. Filtered blood exits kidney through renal vein and then the vena cava. Excretory products and excess water pass into the ureter, and then the bladder for storage. Sphincter muscles control the release of urine from the bladder through the urethra


Ultrafiltration in kidney

The filtration of plasma and substances below a certain size into the Bowman's capsule



Useful components of filtrate reabsorbed into bloodstream from nephron


Process of ultrafiltration in glomerulus

Blood enters the glomerulus by the afferent arteriole and exits by the efferent arteriole. The afferent arteriole has a larger diameter than than efferent arteriole which causes high hydrostatic pressure. Hydrostatic pressure is further increased by the coiling of the capillaries of the glomerulus. Also the proximity to the heart means there is high blood pressure locally.

High hydrostatic pressure forces small components in the blood through the capillaries into the Bowman's capsule (e.g. salts, small proteins, urea, amino acids etc.)
Large components (rbc's, large proteins etc.) remain in capillaries as they are too big to pass through capillary walls.


How does the structure of the capillaries in the glomerulus aid the process of ultrafiltration?

The glomerular capillary cells are a single layer of squamous epithelium cells., with podocytes that extend in two directions to aid the flow of the filtrate. Basement membrane is the effective filter.


What may impose resistance on ultrafiltration?

1. Back pressure builds up in the nephron
2. Osmotic gradient caused by plasma proteins in the glomerulus drawing water backwards.


Selective reabsorption in the PCT

Lining of the PCT is made up of cuboidal epithelial cells that have microvilli and basal invaginations (both increase surface area) and mitochondria. AA's, salts, and proteins are selectively reabsorbed by diffusion and active transport, they then enter the CEC and into the vasa recta. This creates an osmotic gradient that allows for the reabsorption of water. Blood is isotonic as the end of the PCT.


Reabsorption in the loop of Henle

Filtrate travels down descending limb which is permeable to water, then travels up the ascending limb in which cl and na ions are pumped out. This lowers the water potential of the surrounding tissues meaning that more water is drawn out of the the filtrate in the descending limb



All the members of a particular species in a particular place at a particular time


Factors affecting population growth

Birth rate
Death rate


Lag phase

Time taken for nutrient assimilation or egg production or larval development or gestation period, in mammals


Exponential growth phase

Population demonstrating its biotic potential
Numbers increasing by intrinsic rate of natural increase (r).


Stationary phase

As population numbers increase so does competition (and there may be an accumulation of waste) so there is an environmental resistance preventing the population reaching its biotic potential. The population reaches its carrying capacity (K) as the birth&immigration rates equate with the death&emigration rate.


Decline phase

Population has exhausted the resources and/or there is an accumulation of toxic waste so birth rate falls to zero and death rate increases


Characteristics of r-selected species

R for rapid
Short life cycle
Low competitive ability
High dispersal ability
Little parental care


Characteristics of K-selected species

Long lived
High competitive ability
Low dispersal ability
Good parental care



An organism that lives in or on another organism benefiting from it and causing harm over an extended period of time


Pest species

A species that damages a valuable/commercial crop species causing economic damage


Biological control

The deliberate introduction of a predator or a pathogen or a competition or parasite to target the pest species


Advantages of biological control over chemical pestides

No bioaccumulation
No pest resurgence
Broad spectrum pesticides may affect other organisms other than the pest
Lower cost than long term application of pesticides
No pesticide resistance therefore more effective


What are some examples of natural barriers to entry of pathogens in the body?

The skin is an outer protective layer that is tough for pathogens to penetrate given that is is not broken or cut.
Lysosyme is an enzyme found in bodily secretions (sweat, tears, saliva) that hydrolyses the cell walls of a pathogen causing cell lysis and death.
Tears can wash away debris and pathogens from the delicate and easily damaged front of the eye.
Epithelial lining covered in mucus can trap pathogens and prevent them from penetrating the underlying membranes. Cilia in the resp. tract can also bring trapped pathogens back up the trachea.
Hydrochloric acid in the stomach kills most pathogens in food/drink, the low pH denatures the enzymes in the pathogens- kills them.


What happens as part of the inflammatory response following an infection in the capillaries?

The capillaries become leaky allowing the white blood cells to squeeze through to reach the site of infection.


Describe polymorphs

The most common type of WBC and the first to arrive at the site of infection.


Describe macrophages

They develop from monocytes, they are loarger and long lived.


What is an antigen?

Antigens are chemicals that are capable of producing a specific immune response.


Describe the production and maturation of lymphocytes.

Lymphocytes are produced from stem cells in the bone marrow. The B-cells mature in the bone marrow and the T-cells mature in the thymus.


What happens when lympohcyes come into contact with a non-self antigen?

They will become activated and begin to divide rapidly by mitosis.


Describe the mechanism of action of B-cells

B cells are involved in antibody mediated immunity. When they come into contact with a non self antigen on the pathogen itself they divide by mitosis to produce many clones when sensitised- the clones then divide into a variety of specialised B-cells.
Cloned cells divide into plasma cells which synthesise and secrete anytibodies (immunoglobulins)


What is another name for antibodies?



What are immunoglobulins?



In what ways can an antibody work?

Antibodies can cause agglutination of pathogens, clumping them together so that a phagocyte can destroy them by phagocytosis (agglutinins). They can also attach themselves to the pathogen preventing them from entering cells, or they can be antitoxins and neutralise toxins produced by the pathogens.


What are agglutinins?

Antibodies that cause the agglutination of pathogens.


What are the different types of T-cells?

Killer, suppressor, helper and memory.


What do killer t-cells do?

They become activated when they find non self antibodies on the surface of an antigen presenting cell, they, can insert perforins into the antgen presenting cell which can cause the fromation of pores on the membrane of the antigen presenting cell which in turn causes cell death/lysis. They can also introduce hydrolytic enzymes called granzymes which can aid with the destruction of the cell.


What are granzymes?

Hydrolytic enzymes that are secretes by killer T-cells that can aid with the destruction of an antigen presenting cell.


What do helper T-cells do?

They can activate the killer t cells, they can stimulate to eproduction of plasma cells from B-cells to increase the secretiong of antibodies, they can also activate phagocytes to help destroy the cells by phagocytosis.
This is done by secreting cytokines (e.g. interleukin and interferon).


What do memory T-cells do?

They remain in the blood for an extended period of time following a primary immune response so if they come into contact with the antigen again they can divide rapildy killing the pathogens often before symptoms emerge.


What do suppressor T-cells do?

They are sensitive to circulating cytokines and are responsible for deactivating K'T-cells and B-cells preventing an excessive reaction.


What are cytokines?

Cell signalling molecules (proteins, glycoproteins, peptides) which aid cell-to-cell communication in immune responses and can stimulate the movement of cells towards areas of infection and inflammation.



A nitrogeneous compound fromed by the breakdown of AA's and NA's in the liver/



Byproduct of the breakdown of creatine phosphate, important in ATP synth. in muscles.



Stimulates release of acteylcholine and other neurotransmitters making action potentials more likely



Blocks receptors in neuromuscular junctions, loss of muscle function



Blocks calcium ions in pre-synaptic neurone, reducing the amount of neurotransmitter released and action potentials less likely, pain relief.


Purpose of synapses

Unidirectionality (pre-post synaptic neurone direction only, as n'transmitters only produced in pre and receptors only found in the membrane of post.)
Prevent overstimulation, and fatigue, of effectors (N'transmitters used up quicker than produced)


Inhibitory synapses

Cause influx of negative ions into post synaptic membrane (hyperpolarisation) creating an IPSP, making it harder for an action potential to be produced as it is more difficult for the EPSP to reach the threshold level required.



Acetylcholine used in CNS of vertebrates, noradrenaline used in involuntary control (gut movts ect.)
GABA inhibitory


Auxin action

Produced in apical meristem and diffuse down to zone of elongation. Binds to specific receptors in the cell surface membrane of newly formed cells, causing hydrogen ions pumps to pump hydrogen ions into the cell wall. Acidification of cell wall causes the activation of agents such as elastins which loosen linkages between adjacent cellulose microfibrils, making the cell wall more flexible. Water enters the cell by osmosis, causing the formation of a permanent vacuole. This exerts a hydrostatic pressure on the cell wall causing the cell to expand.



Produced in apical buds and leaves, causes elongation of internodal regions.



Produced in apical meristem, stimulate cell elongation on teh zone of elongation



Produced in actively dividing meristematic tissue, stimulates cell division in the zone of division especially with auxins.



All the populations in a particular area at a particular time



A habitat and its associated community includes biotic and abiotic factors and the relationships between them.


Primary succession

Takes place on a previously uncolonised surface.


Climax community

Relatively stable end stage and is in dynamic equilibrium with its environment.


Secondary Succession

Existing ecosystem has been disturbed, fire flooding