excretion

The term metabolism refers to the chemical reactions that occur inside living cells.

Waste products produced by plants include:

The process in plant cells that produces carbon dioxide as a waste product is respiration.

False. Photosynthesis produces oxygen as a waste product. Water is produced as a waste product of respiration.

The intensity of light determines which gas accumulates as a waste product. At high light intensity more photosynthesis occurs so oxygen accumulates, while at low light intensity more respiration occurs so carbon dioxide accumulates.

During the day, with sufficient light for photosynthesis, oxygen is produced in excess and is the main waste product.

False. Plants respire at night and during the day. The difference is that during the day photosynthesis occurs at a higher rate than respiration, so the waste products of photosynthesis accumulate.

Gaseous waste products exit the plant through the stomata in the leaves.

Gaseous waste products exit the leaves of plants by the process of diffusion.

False. The majority of water vapour that is lost in transpiration is not a metabolic waste product, but simply water drawn up from the roots by the transpiration stream.

Excretion is the removal from the body of the waste products of metabolism, and any substances present in excess, e.g. excess salts

Waste products from human metabolism include:

False. Urea is produced during the breakdown of excess amino acids, which come from protein digestion.

The main excretory organs in humans are:

The metabolic waste products excreted by the lungs are water and carbon dioxide, both produced during respiration.

True. A build up of metabolic waste can lower the water concentration of the body fluids, causing water to move out of cells by osmosis.

Waste products are excreted by the skin by the sweat glands when they produce sweat.

False. The kidneys excrete urea, excess water and excess salts. Carbon dioxide is excreted via the lungs.

The main functions of the kidneys are:

Osmoregulation is the process of maintaining the balance of water and dissolved substances, e.g. salts, within the body fluids.

Osmoregulation is important because changes in the osmotic balance between the cells and the body fluids can lead to cells gaining or losing water by osmosis.

False. A high solute concentration occurs when the water concentration is low. When water concentration of the body fluids is low water will move out of the body cells by osmosis down a water concentration gradient.

Losing water by osmosis causes the cells to shrink, or shrivel; this is known as crenation and can lead to inefficiency of cell activity and potentially cell death.

Two processes that will cause an increase in the water content of the body fluids are:

The organ system responsible for the filtration of blood and the production of urine is the urinary system.

False. The liver has a role in many organ systems of the body, but it is not part of the urinary system, which consists of the kidneys, ureters, bladder and urethra.

The four main structures of the urinary system are:

The tubes that connect the kidneys to the bladder are the ureters.

The role of the bladder is to store urine that is produced by the kidneys. Urine exits the bladder via the urethra which removes it from the body.

False. The urethra carries urine from the bladder to the exterior of the body. The ureters are a pair of tubes that connect the kidneys to the bladder.

Nephrons are tiny tubes found in the kidney. Each kidney contains many nephrons, the role of which is to produce urine.

False. Nephrons contain a Bowman's capsule and loop of Henle, as well as several other structures, but do not contain a renal pelvis. The renal pelvis is the region of the kidney into which the nephrons drain.

The sections of a nephron include: Note that the glomerulus is a knot of blood vessels and is not part of the nephron itself.

The knot of blood vessels associated with each kidney nephron is known as the glomerulus.

True. The Bowman's capsule directly surround the glomerulus, a ball of blood vessels from which the blood filters into the nephron.

Ultrafiltration is the process by which molecules are forced out of the blood and into the Bowman's capsule at high pressure.

Ultrafiltration occurs between the glomerulus and the Bowman's capsule.

False. Ultrafiltration occurs at high blood pressure. The narrowing capillaries of the glomerulus increase the blood pressure, forcing small molecules into the filtrate.

Whether a molecule enters the filtrate or remains in the blood during ultrafiltration depends on its size; small molecules are filtered and large molecules remain in the blood.

Substances that are forced out of the capillaries during ultrafiltration are: These molecules form the glomerular filtrate.

Glomerular filtrate is the liquid that enters the Bowman's capsule during ultrafiltration. It contains water, glucose, salts and urea.

False. Glucose enters the glomerular filtrate due to high blood pressure during ultrafiltration. Active transport is not involved in this process.

Reabsorption occurs when substances are taken back up into the blood after having been filtered by the kidneys.

True. Only small molecules are forced into the filtrate during ultrafiltration. Proteins are too large and remain in the blood.

Water reabsorption in the nephron occurs in the following locations:

True. Existing blood water potential determines the volume of water reabsorbed by the kidneys:

Water reabsorption in the kidneys occurs as follows:

True. An increase in salt reabsorption lowers the water concentration of the tissues around the nephron more than usual. This will result in a steeper water concentration gradient and more water will be reabsorbed by osmosis. This water will increase the blood volume and can lead to high blood pressure.

Glucose is reabsorbed from the proximal convoluted tubule.

The proximal convoluted tubule is the first part of the kidney nephron after the Bowman's capsule.

Glucose is reabsorbed on the kidneys by active transport.

The cells that line the proximal convoluted tubule have many mitochondria to release energy for the active transport of glucose.

False. Glucose reabsorption can only occur in the proximal convoluted tubule. This is because glucose transporters are located in this part of the nephron.

True. When blood glucose levels are high the nephron is unable to reabsorb all of the glucose from the filtrate. The glucose is excreted in the urine and can be detected by a glucose test.

Any glucose that cannot be reabsorbed remains in the filtrate and is excreted in the urine.

False. Osmoregulation involves maintaining the balance of water and solutes in the blood. This is achieved by changing the volume of urine produced.

The hormone ADH (antidiuretic hormone) controls water reabsorption in the kidneys.

ADH is produced by the pituitary gland in the brain.

ADH affects the permeability of the collecting ducts to water:

True. If blood water content is too high less ADH is released, leading to less water reabsorption by the collecting duct; this results in production of dilute urine.

If blood water content is too low, more ADH is released, leading to more water reabsorption by the collecting ducts; this results in production of concentrated urine.

True. Drinking lots of water and not sweating on a cool day will result in an increased blood water content. The brain will release less ADH, resulting in decreased water reabsorption and production of dilute urine.

False. High ADH levels cause more water reabsorption; this leads to production of concentrated urine.

The three main components of urine are:

Urea is a waste product formed during the breakdown of excess amino acids from protein digestion.

Increased water intake results in urine that is less concentrated as there is a higher concentration of water in relation to urea and ions.

True. Glucose and protein are not components that we expect to find in urine (the main components are water, ions and urea), so their presence* can* indicate a health condition, e.g. glucose can indicate problems with blood glucose control and protein can indicate kidney damage.