homeostasis and excretion

Question 1

homeostasis

Answer 1

the regulation of conditions inside the body to maintain a stable internal environment, in response to both internal and external conditions

Question 2

excretion

Answer 2

a process in which metabolic waste is eliminated from an organism

Question 3

examples of excretion

Answer 3

the skin excretes water and mineral ions, the lungs excrete carbon dioxide and water, the liver produces urea from amino acids, the kidneys excrete water, mineral ions, and urea

Question 4

what organ plays a major role in both homeostasis and excretion

Answer 4

the kidneys

Question 5

kidneys role

Answer 5

they filter the blood, removing substances and controlling the concentration of water and solutes in the blood and other body fluids

Question 6

internal environment

Answer 6

the surroundings of the cells inside the body, particularly the blood and tissue fluid

Question 7

tissue fluid

Answer 7

a watery solution of salts, glucose and other solutes that surrounds all the cells of the body, forming a pathway for the transfer of nutrients between the blood and cells.

Question 8

how tissue fluid is formed

Answer 8

tissue fluid is formed by the leakage of blood plasma from blood capillaries, it is similar in composition to blood plasma but lacks the plasma proteins and red blood cells as they are too big

Question 9

things that are kept constant inside the body

Answer 9

water levels, salt levels, carbon dioxide levels in the blood, blood pH, concentration of dissolved glucose, and body temperature

Question 10

why homeostasis is important

Answer 10

homeostasis is important because cells will only function properly if they are bathed in a tissue fluid which provides them with their optimum conditions

Question 11

blood plasma and tissue fluid needs to be maintained at

Answer 11

optimum pH 7.35, optimum temperature 37 degrees celsius, correct solute and water concentrations, low waste (urea and CO2)

Question 12

osmoregulation

Answer 12

osmoregulation is how we maintain the correct balance of water and salt/ions in our blood

Question 13

the concentration of solutes and water

Answer 13

the concentration of solutes and water of blood matches the the concentration of solutes and water of tissue fluid

Question 14

homeostasis of cells

Answer 14

animal cells prefer to be in an isotonic state (dilute glucose and salt solution). if tissue fluid has the SAME concentration of glucose and salt outside the cell as inside the cell, then no osmosis will take place (isotonic solution).

If tissue fluid has LOWER concentration of glucose and salt (more water) outside the cell than inside the cell, then osmosis will take place, water will ENTER the cell and it will BURST (hypotonic solution).

if tissue fluid has HIGHER concentration of glucose and salt (less water) outside the cell than inside the cell, then osmosis will take place, water will EXIT the cell and it will become DEHYDRATED and SHRIVEL up (hypertonic solution).

Question 15

urine

Answer 15

an adult human produces about 1.5dm3 of urine every day, although this depends on the amount of water drunk and the volume lost in other forms, such as sweat

Question 16

components of urine (in 1 litre)

Answer 16

23.3g of urea, 0.4g of ammonia, 1.6g of other nitrogenous waste, 10g of sodium chloride (salt), 1.3g of potassium, 2.3g of phosphate

Question 17

nitrogenous waste

Answer 17

meaning they contain the element nitrogen, they are nitrogen compounds through which excess nitrogen is eliminated from organisms. all animals have to excrete a nitrogenous waste product

Question 18

why all animals have to excrete a nitrogenous waste product

Answer 18

carbohydrates and fats only contain the elements carbon, hydrogen, and oxygen. Meanwhile proteins also contain nitrogen.

If the body has too much carbohydrate or fat, these can be stored, e.g as glycogen in the liver or fat under the skin and around other organs.

Excess proteins or amino acids cannot be stored. Amino acids are first broken down in the liver, they are converted into carbohydrate (stored as glycogen) and the main nitrogen-containing waste product, urea.

The urea passes into the blood to be filtered out by the kidneys during the formation of urine. The urea is made by chemical reactions in the cells of the body. Excretion means getting rid of waste of this kind.

Question 19

why faeces aren’t part of excretion

Answer 19

when the body gets rid of solid waste from the digestive system (faeces) this is known as defecation not excretion since it contains few products of metabolism, just the ‘remains’ of undigested food, along with bacteria and dead cells

Question 20

control of body temperature

Answer 20

mammals and birds are homeothermic/endothermic (warm-blooded). these animals keep their body at a constant temperature, for humans this is 37 degrees celsius. metabolic reactions inside the animal produce heat from inside (endothermic). all other animals are poikilothermic/exothermic (cold-blooded). these animals have the same temperature as their environment

Question 21

why it’s important to keep a constant body temp

Answer 21

too cold: enzymes have less kinetic energy, fewer successful collisions between substrates and active site, therefore a slower rate of metabolic reactions

too hot: three-dimensional protein enzymes can have too much kinetic energy, change shape of their active site meaning can no longer bind with the substrate, resulting in denaturing, loss of enzyme activity=loss of metabolism

Question 22

advantage of a human maintaining a body temp of 37 degrees celsius

Answer 22

it means that all the chemical reactions taking place in the cells of the body can go on at a steady, predictable rate

Question 23

monitoring body temperature

Answer 23

the thermoregulatory centre in the hypothalamus monitors our core body temperature. If you are too hot or cold, temperature receptors in the skin send electrical impulses to the hypothalamus which stimulates the brain to alter our behavior.

if changes in behaviour are not enough to keep our body temperature constant, the thermoregulatory centre in the hypothalamus detects a change in the temperature of the blood flowing through it. it then sends signals via nerves to other organs of the body which regulate the temperature by physiological means.

Question 24

functions of the skin

Answer 24

forming a tough outer layer able to resist mechanical damage

acting as a barrier to the entry of pathogens

forming an impermeable surface, preventing loss of water

acting as a sense organ for touch and temperature changes

controlling the loss of heat through the body surface

Question 25

epidermis

Answer 25

the outer layer, consists of dead cells that stop water loss and prevent the entry of bacteria

Question 25

epidermis

Answer 25

the outer layer, consists of dead cells that stop water loss and prevent the entry of bacteria

Question 26

hypodermis

Answer 26

the bottom layer, contains a layer of fatty tissue which insulates the body against heat loss and is a store of energy

Question 27

dermis

Answer 27

the middle layer, contains many sensory receptors (pain, pressure, and temperature), as well as sweat glands and many small blood vessels, it is also where the hair follicle is located. these structures are all involved in temperature control

Question 28

when you are too hot the hypothalamus sends impulses to:

Answer 28

sweat glands secrete sweat: sweat is mostly water, water on the skin’s surface evaporates, this requires energy from your body, water particles use energy from your body to vaporise, your body loses energy and cools down

hair erector muscles relax and hair on your skin lies flat: less air is trapped which means less insulation

blood vessels (arterioles) in the skin dilate (widen): more blood flows to the capillaries near the surface of the skin, the skin looks red, blood carries heat, more heat is lost to the environment by radiation. this is called vasodilation

Question 29

when you are too cold, the hypothalamus sends impulses to:

Answer 29

sweat glands to stop secreting sweat

hair erector muscles contract and hair on your skin stands up: more insulation because warm air is trapped, more useful in hairy animals such as bears since in humans the hairs over most of our body do not grow very large.

blood vessels (arterioles) in our skin constrict (narrow): less blood flows to the capillaries near the surface of the skin, skin looks pale, less heat near the surface and less heat lost, warm blood is diverted towards internal organs. this is called vasoconstriction

Question 30

the urinary system

Answer 30

kidneys filter the blood. unfiltered blood enters the kidneys at high pressure through the renal artery. ‘clean’ blood leaves the kidneys through the renal vein. urine leaves the kidneys through two tubes called the ureters and is stored in a muscular bag called the bladder

Question 31

structure of the kidney

Answer 31

renal artery, renal vein, cortex- outer layer, medulla which contains pyramids, nephrons which run from the cortex to the medulla connecting to the pelvis at the tip of the pyramids where they empty the urine into the pelvis which connects to the ureters carrying the urine to the bladder

Question 32

ultrafiltration

Answer 32

the process where the filter (2 layers of cells and basement membrane) separates different size molecules under pressure.

because of resistance flow caused by the glomerulus, pressure of the blood in the arteriole leading to the glomerulus is very high. This forces the fluid from the blood through the walls of the capillaries and the bowman’s capsule.

Question 33

loop of henle

Answer 33

longer loop of henle= more concentrated urine, more water is conserved in the body

Question 34

control of the body’s water content

Answer 34

when the body loses to much water, the blood becomes more concentrated, this is detected by receptor cells in the hypothalamus. This causes the pituitary gland to release more ADH which travels to the kidneys and causes the collecting ducts to become more permeable to water meaning more water is reabsorbed back into the blood. this makes the urine more concentrated so the body loses less water.