biology4alevel600

Stomata have daily rhythms of opening and closing and also respond to changes in environmental conditions to - allow diffusion of CO­ 2 ­ - regulate water loss by transpiration Stomata open due to: Stomata close due to: high light intensity low concentration of CO­ 2­   darkness high concentration of CO­ 2­   low humidity high temperature water stress Opening and closing of stomata ATP powers proton pumps to actively transport  H + out of cell There is a low concentration of H + and negative charge inside the cell --> K + channels open --> K + diffuse in High concentration of K + inside the cell decreases water potential Water moves in via osmosis Water entry increases the volume of the guard cell, causing it to expand --> open Structure of stomata Each stomatal pore is surrounded by 2 guard cells. Guard cells: open when turgid (gain water) close when flaccid (lose water) Abscisic acid and stomatal closure Abscisic acid (ABA) is a st...

The presence of glucose and ketones in urine indicates that a person may have diabetes . If the concentration for these rises above the renal threshold , then not all glucose has been absorbed from the filtrate in the proximal convoluted tubule --> so will be present in the urine. A large quantity or long-term presence of protein in the urine indicates disease affecting glomeruli kidney infection high blood pressure (can lead to heart disease) 1. Dip sticks : test for glucose, pH, ketones, proteins - urine analysis - involves 2 immobilized enzymes: glucose oxidase and peroxidase - shows the sugar level in urine from bladder NOT the current blood sugar level 2. Biosensor: allows people with diabetes to check their blood to see how well they are controlling their glucose concentration - blood analysis : quantitative data - a pad impregnated with glucose oxidase catalyses reaction to form gluconolactone --> generates tiny electric current that is detected by electrode and ...

Insulin and glucagon work together as part of a negative feedback system. As a result of glucagon secretion, the liver releases extra glucose to increase the concentration in the blood. Muscle cells do not have receptors for glucagon and so do not respond to it. This is question 9, taken directly from the specimen paper for summer 2016 so you won't have to worry about the phrasing :) It is for glucagon but will work fine with adrenaline. (the numbers marked are according to the mark scheme and not the diagram below) 1. glucagon binds to receptors in cell surface membrane (of liver cell) 2. receptor changes conformation 3. G-protein activated 4. adenylate cyclase activated 5. ATP converted to cyclic AMP 6. (cyclic AMP is) second messenger 7. (cyclic AMP) activates kinase protein  8. enzyme cascade: amplifies original signal of glucagon 9. ref. phosphorylase enzyme(s) / glycogen phosphorylase 10. glycogen broken to glucose  11. glucose, diffuses / passes out, of (liver) ...

The blood glucose concentration is regulated by negative feedback control mechanisms. Blood glucose concentration should remain at a fairly constant value of about 100 mg glucose per 100 cm3 of blood. If blood glucose concentration falls well below this level, the person is said to be hypoglycaemic . Cells do not have enough glucose to carry out respiration, and so metabolic reactions may not be able to take place and the cells cannot function normally. This is especially so for cells such as brain cells, which can only use glucose and not other respiratory substrates. The person may become unconscious and various tissues can be damaged. If blood glucose concentration rises well above this level, the person is said to be hyperglycaemic . The high glucose concentration decreases the water potential of the blood and tissue fluid, so that water moves out of cells down a water potential gradient. Again, unconsciousness can result. Several hormones are involved in the control of blood glu...

Osmoregulation is the control of the water content of body fluids. It is part of homeostasis, the maintenance of a constant internal environment.  It is important that cells are surrounded by tissue fluid of a similar water potential to their own contents, to avoid too much water loss or gain which could disrupt metabolism. You have seen that water is lost from the fluid inside a nephron as it flows through the collecting duct. The permeability of the walls of the distal convoluted tubule and collecting duct can be varied. If they are permeable, then much water can move out of the tubule and the urine becomes concentrated. The water is taken back into the blood and retained in the body. If they are made impermeable, little water can move out of the tubule and the urine remains dilute. A lot of water is removed from the body. ADH ADH is antidiuretic hormone . It is secreted from the anterior pituitary gland into the blood. When the water potential of the blood is too low (that is,...

Ultrafiltration occurs at the barrier between the blood and the filtrate in the renal capsule or Bowman's capsule in the kidneys. Ultrafiltration The Bowman's capsule contains a dense capillary network called the  glomerulus . Blood flows into these capillaries through the afferent arteriole and leaves through the efferent arteriole . The blood in a glomerulus is separated from the space inside the renal capsule by: • the capillary wall ( endothelium ) which is one cell thick and has pores in it; • the  basement membrane  of the wall of the renal capsule; • the layer of cells making up the wall of the renal capsule, called  podocytes ; these cells have slits between them. The blood in a glomerulus is at a relatively  high pressure , because the efferent arteriole is narrower than the afferent arteriole. This forces molecules from the blood through these three structures, into the renal capsule.  The pores in the capsulary endothelium and the slits betwe...

The kidneys remove wastes from the blood and are the effectors for controlling the water potential of the blood. The removal of waste products generated by metabolic reactions inside body cells is called  Excretion . Some of these products are toxic, while others are simply in excess of requirements. In mammals, the 2 major excretory products are: CO2 produced by aerobic respiration. CO2 dissolves in H2O to produce a weak acid, so if too much builds up in body fluids the pH drops, which can damage cells and disrupt metabolism. CO2 is transported to the lungs dissolved in blood plasma and excreted in expired air. Nitrogenous excretory products , in particular urea . Excess amino acids cannot be stored in the body. In the liver, they are converted to urea,  CO(NH 2 ) 2 ,  and a keto acid . The keto acid can be respired to provide energy, or converted to fat for storage. The urea dissolves in the blood plasma and is removed and excreted by the kidneys. The structure and...

One of the most important examples of homeostasis is the regulation of body temperature . It involves both coordination  systems - nervous and endocrine. Not all animals can do this physiologically. Endotherms - Animals (e.g. birds and mammals) that have a constant  body temperature at around 35 - 40°C, also called warm-blooded animals.   - Use  internal corrective  mechanisms to maintain body temperature.  Ectotherms  - Animals that have a  variable  body temperature. - Use  behavioural  mechanisms (e.g. lying in the sun when cold, moving into shade when hot). Such mechanisms can be very effective, particularly when coupled with internal mechanisms to ensure that the temperature of the blood going to vital organs (brain, heart) is kept constant.  We use both! Thermoregulation All mammals generate heat and have ways to retain it within their bodies. They also have physiological methods to balance heat gain, retention ...