Excretion and transport in other organisms

Unit 1 Area of Study 2 – transport systems

Excretion in Freshwater Fish

Unlike in humans, fish have a ready supply of water to dilute nitrogenous wastes

In freshwater fish, water moves readily into the gills (why?). This water is then used to flush wastes out of the fish, in a dilute urine

Excretion in Saltwater Fish

Because saltwater fish drink seawater, and this has a large quantity of salt in it, salt is absorbed into the fish’s body. This salt is then pushed back to the gills, and back into the surrounding water. Any ammonia wastes leave with this salt via the gills

Saltwater fish produce a very small amount of concentrated urine, which contains salts and some urea

Excretion in insects

Insects have tubes called Malpighian Tubules, which float in the blood. They collect nitrogenous wastes, which are formed into uric acid crystals (like hardened urea), which enters the intestine and is excreted via the anus.

Comparing excretory systems in animals

Characteristic Human Fresh water fish Salt water fish Insect

Structure that filters waste from blood

Nephrons in kidneys

Nephrons in kidneys

Nephrons in kidneys and gills

Malpighian tubes

Length of loop of Henle

Long Virtually none Long Not applicable (no kidneys!)

Type of urine (in relation to normal body fluids)

Hypertonic (high salt concentration)

Hypotonic (low salt concentration)

Isotonic (the same salt concentration)

Extremely hypertonic (crystals – no water content)

Main nitrogenous waste excreted

Urea Ammonia (some urea too)

Ammonia Uric acid crystals

Comparing animal transport systems (circulatory)

Feature Mammal Fish Insect

Nature of system Blood enclosed in vessels that don’t directly contact tissue cells

Blood enclosed in vessels that don’t directly contact tissue cells

Open system in which blood directly bathes tissue cells

Oxygen carrier Pigment in Red Blood Cells (haemoglobin) – high oxygen carrying capacity

Pigment in Red Blood Cells (haemoglobin) – high oxygen carrying capacity

No function in carrying oxygen in this system

Carbon dioxide carrier In plasma is bicarbonate ions. Some can bind to haemoglobin

In solution in plasma No function in carrying carbon dioxide

Nutrient carrier In solution in plasma In solution in plasma In solution in colourless blood

Pumping mechanism Four-chambered heart Two-chambered heart Single tube heart

Number of times blood travels through heart

Twice per circulation within the body

Once per circulation within the body

Once per circulation within the body

Transport in Plants

We have already briefly looked at phloem and xylem, and what they do.

Xylem – transports water from the roots to other parts of the plant

Phloem – transports glucose and other minerals around the plant, from the site of photosynthesis

How do Xylem work?

Xylem can use capillary action (the fact that water molecules stick together and stick to the tube’s walls) to move small amounts of water

However, the quantity of water that needs to be moved, and the direction it is moved in, means that some energy is consumed in the movement of water around the plant

This energy is provided by sunlight

Xylem continued…

Gases enter and leave the leaves via stomata. Water vapour also leaves via the stomata, in a process called transpiration.

The cells within the leaf lose their water when the stomata open. In turn, they are replenished by the xylem opening, and this water can then be lost through the stomata

An animation might help?

http://www.sciencemag.org/sciext/vis2005/show/transpiration.swf

What about phloem?

Soluble organic substances are transported by phloem. This includes glucose.

Organic substances may be moved for use in another area of the plant, or for storage for later use

The movement of these substances around the plant is called translocation.

Translocation requires energy

Use of sugars

Many plants store sugars in the form of starch (eg. Potatoes, bananas), for break down and use for energy at another time.

Sugar can be used to build the subunits of cells

Or it can be used as the energy source in cellular respiration

Gas exchange in plants

Stomata in the leaves open, allowing for movement of gases in and out of the leaf, by diffusion.

Remember: the opening of the stomata depends on the hardness (turgor) of the guard cells. The higher the water content, the harder the cells. Water enters the guard cells via osmosis.

Other plant gas exchange sites

Lenticels – Small gateways in the stem for gas exchange. Cells are loosely packed in these areas and so gases like oxygen and carbon dioxide can get through.

Root hair surface gas exchange – as well as diffusion of water, some gases diffuse into and out of the plant through the root hair surfaces.

Excretion in plants

Plants do not have advanced excretory systems, as they can tolerate some fluctuations in their environment. They tend to instead store wastes in insoluble forms, in vacuoles. These can be shed without detriment to the plant.

Mammals vs Plants

Large intake of food means a large amount of waste produced. Mammals need to ingest their nutrients, while plants largely make their own food, and so mammals need more advanced excretory systems for large amounts of waste.