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 CharacteristicHumanFresh water fishSalt water fishInsect Structure that filters waste from blood Nephrons in kidneys Nephrons in kidneys and gills Malpighian tubes Length of loop of Henle LongVirtually noneLongNot 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 UreaAmmonia (some urea too) AmmoniaUric acid crystals

Comparing animal transport systems (circulatory) FeatureMammalFishInsect Nature of systemBlood enclosed in vessels that don’t directly contact tissue cells Open system in which blood directly bathes tissue cells Oxygen carrierPigment in Red Blood Cells (haemoglobin) – high oxygen carrying capacity No function in carrying oxygen in this system Carbon dioxide carrierIn plasma is bicarbonate ions. Some can bind to haemoglobin In solution in plasmaNo function in carrying carbon dioxide Nutrient carrierIn solution in plasma In solution in colourless blood Pumping mechanismFour-chambered heartTwo-chambered heartSingle tube heart Number of times blood travels through heart Twice 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? ow/transpiration.swf ow/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.