Explain the difference between each of the following pairs of terms. Excretion and egestion.

Excretion Egestion It is the removal of metabolic wastes from the body. It is removal of undigested food material from the body. It is associated with kidneys. It is associated with alimentary canal. The matter that is egested is faeces. The materials that are excreted are sweat, urine or carbon-dioxide. It takes place through anus and sometimes through mouth. It takes place through urethra, skin or mouth.

The diagram represents several different types of molecules in solution separated by a membrane. (b) Explain the processes by which molecules move through the membrane.

In the diffusion, substance moves from an area of higher concentration to lower concentration (into the cytoplasm) through a permeable membrane. The passive transports form of diffusion and osmosis are to move materials of small molecular weight across membranes.

The diagram below shows what happens during filtration in the glomerulus of a kidney. Explain how filtration differs from the processes of which molecules move through the membrane?

Diffusion and osmosis depends on concentration gradient while filtration uses a pressure gradient. Active transport moves molecules and ions from lower concentration to higher concentration with the help of energy in the form of ATP. Filtration is non-specific. It means, it passes molecules due to pressure gradients and their size. Sometimes the rate of diffusion is enhanced by pressure, causing the substances to filter more rapidly.

The diagram below shows what happens during filtration in the glomerulus of a kidney. (f) Explain what happens to molecules in the filtrate before urine leaves the kidney.

The fluid in the renal capsule is a solution of glucose, salts and urea are dissolved in water. All the glucose, some of the water and some of the salts need to be kept in the blood. Useful substances from the fluid in the kidney tubule are reabsorbed and pass back into the blood in these capillaries. The remaining fluid continues on its way along the tubule. By the time it gets to the collecting duct, it is mostly water with urea and salts dissolved in it. It is called urine.

E M B I B E

Cambridge IGCSE® Biology Coursebook Third Edition>Chapter 12 - Excretion>End-of-chapter questions>Q 3

MEDIUM

Upper Secondary: IGCSE

IMPORTANT

Earn 100

The diagram below shows what happens during filtration in the glomerulus of a kidney.

(d) Name the molecules that pass out of the blood plasma.

Important Questions on Excretion

HARD

Upper Secondary: IGCSE

IMPORTANT

Cambridge IGCSE® Biology Coursebook Third Edition>Chapter 12 - Excretion>Questions>Q 12.3

What happens to the excess protein you eat?

HARD

Upper Secondary: IGCSE

IMPORTANT

Cambridge IGCSE® Biology Coursebook Third Edition>Chapter 12 - Excretion>End-of-chapter questions>Q 1

Copy and complete these sentences, using some of the words in the list. You may use each word once, more than once or not at all.

Absorption, amino acids, digestion, dioxide, fatty acids, ingestion, kidneys, liver, lungs, metabolism, monoxide, respiration, stomach, urea, urine, waste products

Excretion involves the removal of _______ ________ of _______ from the body. Carbon _______ is produced by all cells during _____ and is excreted by the ______. Urea is produced in the ______ from excess _______ _______ and is excreted by the ________, dissolved in water to form ____.

HARD

Upper Secondary: IGCSE

IMPORTANT

Cambridge IGCSE® Biology Coursebook Third Edition>Chapter 12 - Excretion>End-of-chapter questions>Q 2

Explain the difference between each of the following pairs of terms.