um we're going to look at nutrient and gas requirements so we're going to look at the xylem and phloem we're going to look at respiratory systems in different organized organisms and circulatory systems in different organisms as well okay moving on to the gills so the paired respiratory respiratory organ of fish and some amphibians by which oxygen is extracted from water flowing over surfaces within or attached to the pharynx right so we're looking at the walls of the pharynx and we're going from there so um water flows into the gills uh into the gill slits of in the side of the fish um so if you've seen a fish before in the structure of it you know that they've got gills on the side um and then deoxygenated blood moves into the secondary lamellae in preparation for the water to flow in. Then we've got oxygen is then absorbed from the water into the lamellae, which moves into the blood, and then carbon dioxide is released. Okay, so like in humans, blood is then pumped back in to the fish using the heart. So in that way, it's similar to humans.
We've then got the high SA increases, the rate. of the gas exchange. So that is a macroscopic gas exchange and we can see the diagram there of the gills.
Moving on, we've then got the trachea. So we're looking at a large membranous tube extending from the larynx to the bronchial tubes and conveying air to and from the lungs, the windpipe essentially. that is another form of gas exchange when we see that macroscopic.
We can see outside insect and inside index. We've got the trachea. We've got the spiracle.
We can go from there. So gas exchange occurs directly onto the cells of the organism versus closed. Okay so blood and intestinal fluid, so the fluid that surrounds the cells, is pumped into different vessels. So in insects air flows through a small opening in the body called spiracles, right?
So that's where the actual air comes in from. It then goes into the trachea and then into the small branching structures, okay? And we can see them here. So it goes into the trachea here and then it goes into the smaller structures that you can see here.
Into the cells, the tracheals branch into every cell in the body. allowing oxygen and water to diffuse in and carbon dioxide to diffuse out. Okay. So the movement of air occurs through passive diffusion, like we went through over here, passive movement of materials, diffusion, or active ventilation, where larger insects contract their internal organs and abdomen and then to force air out so it just depends on the size of the insect as well so something to consider sorry something to consider there digestive system so we've got the mouth which is physical digestion so teeth chew tongue shapes food increases sa for chemical digestion so the enzymes sort of break down um the starch they sort of begin that breakdown so enzymes are known to break down that starch.
And then we've got the oesophagus, we've got the bolus, so we've got the breakdown of starch then continues through the epiglottis then blocks the respiratory system. We've got the stomach, we've got of course physical digestion, so you sometimes you hear your stomach churning, that's what it's doing, it's digesting, it's relaxing. You've got gastric juices that combine with the food.
and then you've got macromolecules which actually which are broken down into their building blocks we've got the small intestine which we move down into the small intestine and what we've got is three regions um so the the chyme from the stomach causes the release of pancreatic juices and the large intestine aids with the absorption of the nutrients and converts the food and then it comes out through your faeces. So beneficial bacteria in the large intestine actually helps to digest these substances and some substances such as water and ions are released and used for metabolism. So that is sort of a summary of what is actually involved in the digestive system.
So hopefully that is making sense. Okay, so the remainder of the digested material will then, from the small intestine, which is over here. Oh, sorry, which is over here.
will then move into the large intestine, which is over here. So this includes water, salts, dietary fibre, whatever. So vitamins A and K are then produced by the large, also get absorbed into the bloodstream. So there you go.
That's a sort of summary of the digestive system. Moving on to the xylem structure. Xylem's vessels are long, water-filled tubes consisting of elongated cells joined end-to-end. So as the cell matures, the cell wall is strengthened with lignin, which makes them more rigid than they were.
So over time, when it matures, it sort of gets more rigid. The cytoplasm and nucleus in the xylem vessel cells then disintegrate and the cells die. So they're creating hollow lignin tubes.
Mature xylem vessels, so... perforated or complete openings at each end kind of like a straw so that fluid can flow directly through it so we've got pits which are unthickened areas and perforations in the side walls allow sideways movement of substances between neighboring vessels in the vascular bundle right so no nucleus or cytoplasm exists here so the trichids are single large tapering water-filled cells that form part of the xylem tissue in all vascular plants. So when mature they lose their nucleus and cytoplasm. So this leads to the cell death but creates an open structure for water to flow through it. Then we've got mature tracheids.
So cylindrical skeletons of dead cells actually join together to form continuous tubes. So unlike xylem vessels, trichids are not connected end to end. And so instead their ends overlap and water is transferred horizontally through adjoining pits. So those are some of the key terms that we need to understand in the xylem structure. Moving on to the phloem structure.
So phloem tissue is composed of the sieve tubes, the companion cells. the parenchyma cells and the sclerenchyma cells as well. So we've got the phloem structure, as we can see over here. Unlike xylem cells, mature phloem sieves tubes are living cells, so they have no nucleus or no lignin in their cell walls.
So that's a difference, right? You want to understand the difference between the two because you may be asked that in an exam. Sieve tubes form linear rows of elongated cells. Their cell walls are thin and perforated by each end by holes or pores which form sieve plates. So the plasmodesmata pass through the perforations of the sieve tubes and they act like straws through which water and other materials can actually move.
So it's very interesting how it actually differs from the xylem structure and what the different elements are. So let's go through definitions. So sieve tubes, they provide structural support, work with companion cells to transport the molecules, as we talked about.
Companion cells, they enable transportation of these sugars. Then we've got the parenchyma cells which provide structure to the vascular tissue. The sclerenchyma cells provide structural support to the actual phloem and the plasma desmata cells enable the transport of the actual molecules.
So each one has a structure and it's important to memorise and understand what each structure is and how to approach it. So macroscopic structures in animals looking at fish. So single circuit of blood flow.
So blood flows from the gills straight to the capillaries rather than passing through the heart. Versus in mammals who have a double cycle circulatory system. So understanding in different types of animals what the different types of systems are.
So the heart has two chambers. So blood is pumped to the gills for gas exchange versus lungs. So this enables fish to regulate one circuit of blood flow.
So you can see gill capillaries, the heart, the body capillaries, the water and the blood within the fish. It's a single circulatory system compared to the double. So open circulatory system, this essentially means that they have dissolved nutrients that travel directly to tissues rather than remaining in blood vessels. Right so the heart, you've got back end of the dorsal vessel.
okay, divided into the chambers called the ostia and the contract to push it forward. Okay, so we can see the dorsal vessel as a tube running longitudinally in the insect, which is responsible for transporting the material from the abdomen to the head. And then we've got the aorta.
which is the front part of the dorsal vessel, okay, tube leading to the head where it empties and then we've got after emptying it really travels through the organism. So it's important to have a look and sort of see. So we've got the ostea over here, the heart over here, the dorsal diaphragm over there, so just understanding where everything is in the insect as well. All right.