Exceretion And Elimination

Question 1

Define excretion

Answer 1

Excretion is the removal of ‘waste’ products by an organism
• Excretion regulates the internal environment in three main ways: (i) controls cell/body water content
(ii) maintenance of solute composition, and
(iii) excretion of metabolic waste products and other unwanted substances

Question 2

What is secretion?

Answer 2

Secretion is the movement of material that has a specific task after leaving the cell or organism.

Question 3

What is the elimination?

Answer 3

Elimination - the removal of unabsorbed food that has never been part of the
body, typically in the form of faeces.

Question 4

Why is excretion and elimination important?

Answer 4

An inability to remove excretory or waste products can lead to disruption of cell membranes, inefficient metabolism and may lead to death

Question 5

What is passive transport?

Answer 5

Where solutes cross the membrane without the involvement of a specific transport protein.
• movement of solutes (proteins, amino acids or other biproducts) occurs due to the chemical gradient of the solute and thus through osmosis and diffusion.
• Common in bacteria, fungi and to some degree aquatic plants

Question 6

What is active transport?

Answer 6

Most species have specialized cells or organs that have evolved to assist with excretion and elimination.
• Active transport of waste products allows for organisms to be larger and more complex in size.

Question 7

Specialised cells that assist with excretion: animals

Answer 7

Flame cells - specialized excretory cells found in freshwater invertebrates (e.g. rotifers, flatworms)
• Flame cells function like the mammalian kidney – they remove waste materials
• Bundles of flame cells are called protonephridia

Question 8

Specialised organs in animals that assist with excretion

Answer 8

Animals have evolved a range of organs that assist specifically with excretion
• Early animals (aquatic flatworms) have protonephridia
• Later animals (annelids and arthropods) have evolved
more complex nephridia, along with associated glands
• Vertebrates have kidneys and a liver (along with associated glands)

Question 9

Triploblasts: the importance of the coelom

Answer 9

Fluid-filled so can be used as internal support
• Separates internal processes from gut
• Allows transport of fluids (circulatory and excretory systems)
• Provides space for development of internal organs
• Enables increased body size

Question 10

Excretion in protists and early eukaryotes

Answer 10

Single-celled organisms have just the one cell to play with and there are no specialised organs.
The majority of waste and biproducts of metabolism are eliminated by passive diffusion and osmosis.
Active transport of waste (chemicals) occurs through specialised membrane channels and/or are expelled directly.

Question 11

Excretion in protists and early eukaryotes

Answer 11

Following endocytosis, amoeba digest the food particle by releasing enzymes into the food vacuole.
Post-digestion, waste is expelled in a reverse process to phagocytosis called exocytosis.

Question 12

Excretion in Fungi

Answer 12

Fungi also have no specialised organs to excrete waste
Some waste and biproducts of metabolism are eliminated by passive
diffusion and osmosis.
Active transport of waste (chemicals) occurs through specialised membrane channels and/or are expelled directly using a comparable method to bacteria (exocytosis with food vacuoles – or contractile vacuoles).
Life’s Complexity Topi

Question 13

What are the three main mechanisms of excretion and elimination in plants?

Answer 13

Transpiration: Gaseous wastes and water are excreted through stomata, lenticels of the stem, and the outer surface of the stem or fruits
Storing: Some organic waste is stored in plant parts such as bark and leaves
Diffusion:Aquaticplantsexcretemetabolicwastesthroughdiffusion. Terrestrial plants excrete into the soil.

Question 14

What is guttation?

Answer 14

drops of xylem (carries water) sap gather on the tips or edges of leaves of some plants and a number of fungi
Guttation usually happens at night when the stomata are closed and water builds up due to root pressure

Question 15

Where do plants store their waste?

Answer 15

Plants produce their waste materials which get accumulate in the vacuoles of Ageing cells . These storage structures cam be stems, leaves or banks of trees, these cells eventually die and full off.

Question 16

How do different animals excrete different nitrogenous waste?

Answer 16

° aquatic animals convert it to ammonia, terrestrial species convert it to urea or uric acid while spiders convert it to guanine.

Question 17

What are the advantages and disadvantages associated with the excretion of different nitrogenous waste?

Answer 17

Ammonia (one N per molecule) - requires lots of water for excretion and is very toxic. However, it is extremely soluble and no energy is expended in its synthesis.
• Urea (two N per molecule) - less toxic and requires less water for excretion, but its synthesis is more complex and has a metabolic cost of four ATP molecules per molecule of urea.
• Uric acid (four N per molecule) - highly insoluble and non-toxic, so its excretion conserves water, but its synthesis is more complex and entails a higher metabolic cost of 24 ATP molecules per molecule of uric acid.
• Guanine (five N per molecule), is also nearly insoluble and can be excreted with little water loss, but it comes at a high energy cost.

Question 18

Explain the excretory organs in invertebrates?

Answer 18

Excretory organs in invertebrates (including annelids or insects) transport waste from the coelom to the exterior.
• The excretory organs increase in complexity from simple protonephridia (found in marine worms) the more complex nephridia (earthworms and some insects) and the Malpighian tubule system (found in many insects and spiders).
• In insects (and birds and reptiles), the hindgut is involved in both excretion and elimination; N waste first moves into it prior to excretion (usually mixed with faeces).

Question 19

Explain the excretory organs in animals?

Answer 19

The Kidneys – These are the primary excretory organ of vertebrates although various other organs, including the skin, gills and gut assist with solute and water regulation
The Liver - is an important organ of excretion in vertebrates. It breaks down many substances in the blood, including toxins, and assists with the breakdown of red blood cells.
In birds and reptiles, excretion and elimination of waste occurs from the hindgut via a single opening (the cloaca); mammals have a separate opening for each.