excretion

Question 1

define the process of excretion

Answer 1

removal of metabolic waste from an organism
metabolic waste refers to by products of chemical reactions within the organisms

Question 2

what is the difference between egestion and excretion

Answer 2

egestion is the removal of undigested food from the body through the anus in the form of faeces
difference is substances being removed

Question 3

why is excretion important

Answer 3

waste will accumulate and become toxic to cells without excretion

Question 4

how does excretion occur in unicellular organisms

Answer 4

unicellular organisms for example amoeba have a large surface area to volume ratio
simple diffusion of excretory products across cell membrane out of cell takes place

Question 5

explain excretion in plants

Answer 5

plants do not have excretory organs like humans do
carbon dioxide oxygen gases and water vapour diffuse out of leaves through stomata and out of the trunk through lenticels
tannins bitter chemical nitrogenous compounds are stored mainly in the trunk of trees
usually found in bark but can also be stored in leaves buds stems fruits seeds and roots
calcium oxalate and nitrogenous compounds are converted into insoluble substances such as crystals or oil droplets and are stored in dead permanent tissue of the plant
when the plant sheds these structures waste products are removed

Question 6

what are the excretory products in plants

Answer 6

calcium oxalate
tannins
water
carbon dioxide
oxygen

Question 7

what are some of the excretory products stored in these plant tissues that are useful to humans

Answer 7

rubber latex dyes oils

Question 8

what are the excretory products in animals

Answer 8

carbon dioxide
water
ions
bile pigments
nitrogenous waste
heat

Question 9

explain excretion in animals

Answer 9

animals have specific excretory organs to get rid of waste products
the lungs secrete carbon dioxide and water vapour during expiration
the liver excretes bile pigments and is the site of deamination where nitrogenous wastes are produced
kidneys excrete nitrogenous waste made in the liver water salts in the form of urine
skin secretes water nitrogenous waste and salts in the form of sweat as well as excretes excess heat

Question 10

describe the external structure of the kidneys

Answer 10

humans have two each of which is red bean shaped

Question 11

where are the kidneys located

Answer 11

in the lower back region of the body

Question 12

how does blood travel to and from the kidneys

Answer 12

to via the renal artery
leave via renal vein

Question 13

explain what happens to urine

Answer 13

stored temporarily in the bladder which then leaves via the urethra and exits the body

Question 14

how is each kidney connected to the bladder

Answer 14

by a tube called the ureter

Question 15

describe the nephron

Answer 15

the basic unit of structure and function of the kidney
small tubule made up of six general regions
glomerulus
bowman’s capsule
proximal convoluted tubule
loop of henle
distal convoluted tubule
collecting duct

each nephron filters waste from the blood and produces urine which is taken to the bladder to be excreted
nephron spans the cortex and medulla
loop of henle extends into the medulla while other structures are found in the cortex region of kldney

Question 16

how many nephrons are there in each kidney

Answer 16

1 million
means there are more 2 million nephrons working to produce urine
this makes process very efficient

Question 17

explain the process in the glomerulus

Answer 17

it is a knot of capillaries which is enclosed by the bowman’s capsule

blood enters via the afferent arterial and leaves via the efferent arteriole
diameter of afferent arteriole is larger than that of the efferent arteriole
this creates an increase in blood pressure as the blood moves into the capillaries in the glomerulus
this causes blood plasma to squeeze through spaces in capillary walls exiting the glomerulus
dissolved substances small components of blood and blood plasma – called filtrate

this process is known as pressure filtration or ultrafiltration

Question 18

explain the process in the bowman’s capsule

Answer 18

filtrate does not contain any blood cells or blood proteins since these are too large to cross capillary walls
filtrate contains water mineral salts glucose vitamins amino acids urea
filtrate passes down from the bowmans capsule into pct

Question 19

explain process in the proximal convoluted tubule

Answer 19

this region of the nephron tubule just below bowmans capsule is very twisted
efferent arteriole branches into various capillaries which form a network around pct
main role is selective reabsorption
important and useful components of the filtrate such as all glucose amino acids vitamins and some salts are reabsorbed across pct wall across the capillary wall and back into the blood for use by the body
waste products remain in the tubule and move along to the loop of henle

Question 20

explain the process of loop of henle

Answer 20

this region is u shaped
main function: reabsorption of water from the filtrate back into the blood
the longer the loop the more surface area is available for water reabsorption
some animals such as the kangaroo rat which live in very hot climates have extremely long loops of henle for maximum water conservation

Question 21

explain the process of distal convoluted tubule

Answer 21

main function selective reabsorption of mineral ions and water
convoluted nature of tubule increases surface area available for reabsorption
unlike pct, its walls are not made up of cells with microvilli

Question 22

explain the process in the collecting duct

Answer 22

has many branches each connecting to a nephron
collects filtrate from dct and plays a role in reabsorption of water
filtrate is now called urine: excess water, excess salts, urea
transported along collecting ducts which carry the urine to ureter which then takes the urine to bladder for temporary storage

Question 23

define osmoregulation

Answer 23

maintenance of constant osmotic pressure in the fluids of an organism by the control of water and salt concentrations

Question 24

what affects how much water is reabsorbed by the kidneys

Answer 24

antidiuretic hormone
ADH

Question 25

what occurs if the blood is too concentrated

Answer 25

hypothalamus sends a message to pituitary gland stimulating it to secrete adh travels through blood to kidneys where increases the permeability of dct and collecting duct walls to water causes more water to leave dct and collecting ducts and be reabsorbed by blood this causes concentration of blood to return to normal small amounts of conc urine will be produced

Question 26

what occurs if the blood is too dilute

Answer 26

hypothalamus sends a message to the pituitary gland stimulating it to secrete less ADH less ADH travels through the blood to kidneys so DCT and collecting duct are less permeable to water this causes less water to leave the DCT and collecting ducts and be reabsorbed by blood causes concentration of blood to return to normal large amounts of dilute urine will be produced

Question 27

what happens to the skin when it is hot

Answer 27

vasodilation: arterioles dilate so more blood enters skin capillaries and heat is lost sweating: sudorific glands secrete sweat which removes heat when water changes state pilorelaxation hairs flatten stretching out: opens up the body has a larger surface area hair muscles relax hair lies fast so heat can escape sweat secreted by sweat glands cools skin by evaporation blood flow in capillaries increases

Question 28

what happens when the skin is cold

Answer 28

vasoconstriction: arterioles get smaller to reduce blood going to skin keeping core warm shivering: rapid contraction and relaxing of skeletal muscles heat is produced by respiration piloerection: hairs on skin stand up curling up : making yourself smaller so smaller surface area hair muscles pull hairs on end erect hairs trap air blood flow in capillaries decreases