PASS THE BOOK!!!! Write what you can about how organisms exchange materials with their environment Pass the book every 30 seconds (+5 seconds per pass) and keep adding to what has been written. Good luck!!!

Highlight what in your book relates to what you may think the lesson is about (use the picture as a clue ... ;)....)

Specification points Candidates should know: Gas exchange across the gills of a fish (gill lamellae and filaments including the counter-current ) Candidates should be able to use their knowledge and understanding of the principles of diffusion to explain the adaptations of gas exchange surfaces.

Learning Outcomes Revise the structure of the fish gill Revise the difference between parallel flow and counter-current flow Revise how counter current flow increases the rate of gas exchange EXAM QUESTION PRACTISE!!!! (I’ll try to make it fun... Promise!!)

How is the structure of the gills related to its function? Think: Specialised exchange surface SA/V ratio Fick’s Law Gas Exchange Blood flow

Gas exchange in Fish Gas exchange in fish occurs in the gills The gills are supported by a gill bar/arch Gill bars are made of bone or cartilage The space between the gill bars is called gill slit Each gill has two rows of filaments The filaments are covered with folds called lamellae Where exactly gas exchange occurs Pharynx

Diffusion As the water passes through the gills the gas exchange occurs in the lamellae In the lamellae, the distance between the water and the blood cells is 5µm The distance between two lamellae is 50µm. Water prevents them from collapsing Gills provide a large surface area (think about the filaments and lamellae). Gills have an extensive network of blood capillaries to maximise the diffusion Haemoglobin is used to carry the oxygen Ideal for diffusion

Ventilation Fish swims forward with the mouth open Fish can ventilate: - passively - actively (bony fish) MORE EFFICIENT 1 Mouth opens & operculum closes 2 Buccal floor lowers so the buccal cavity volume increases. As the volume increases the pressure decreases and the water flows in (like a suction pump). 3 Mouth closes 4 Buccal floor raises so the pressure increases 5 Operculum opens so the water is pushed out through the gills Fish point their mouth upstream

Bony or cartilaginous?

Counter-current flow VS Parallel flow READY TO BECOME ONE WITH THE FISH?? 

YOUR PARTS: X 4 - water molecules X 4 – Blood molecules X 4 – gill lamellae x 1 - mouth BECOMING A FISH EXCHANGE SURFACE!!! Pupils to become   1x fish mouth (hula hoop) 6x water molecules 6 x blood molecules Remaining pupils (hopefully 6) lamellae Ping pong balls (36) Large sheets of paper (filaments) Demonstrate counter and parallel flow. Parallel flow – pupil holding hula hoop “opens” the mouth by enabling “water molecules” to enter. “blood molecules” should flow in the same direction. Water molecules should be holding 6 ping pong balls each... These represent oxygen. By water and blood flowing the same direction, when the water has passed three oxygen to the blood (via the lamellae) to which it is walking along beside, no more exchange should happen as there is no longer a diffusion gradient. Counter flow – the blood flows in the opposite direction to the water molecules coming through the mouth. This means each blood molecule should pass each water molecule, enabling collection of 6 ping pong balls (representing full saturation) and demonstrating the benefit of the counter flow system.

Counter current flow Parallel flow Bony fish Cartilaginous fish

EXAM QUESTION PRACTISE In pairs, you will be issued an exam question. You will be given 5 minutes on this question – jot notes around it relevant to the question you think may be needed to get exam points. If your question is in parts make sure you label the info clearly. Write relevant past paper exam questions for particular exam board on large A3 sheets for pupils to write on and add to.

EXAM QUESTION PRACTISE After 5 minutes we will undertake a circus rotation. Move on to the next question – you will be given 2 minutes to add to the info already there. After two minutes you will move on to the next question and so on... More info later...

PLENARY In your pairs: Use the info on your question sheet to write a model answer for the given exam question! All answers will be typed up and copied for each of you to have a copy next lesson. GOOD LUCK!!!