6.1 Gas exchange

Learning objectives To DESCRIBE the relationship between the size of an organism or structure and its surface area to volume ratio To EXPLAIN the changes to body shape and development of systems in larger organisms as adaptations that facilitate exchange as this ratio reduces? To EXPLAIN the relationship between surface area to volume ratio and metabolic rate?

The Big questions THE BIG QUESTION: How does surface area to volume ratio impact on living organism’s ability to exchange gases and issues arising with gas exchange?

Preparatory notes recap What is required for gas exchange to take place efficiently? What is the surface area to volume ratio of these cubes? Surface area Volume SA:Vol ratio Take it further Giving two reasons, explain why the blocks above are not a good model for describing the problems with surface area:volume ratio in organisms

Preparatory notes recap What is required for gas exchange to take place efficiently? a large surface area over which gas exchange may take place rapidly a concentration gradient down which gases may diffuse a thin surface across which gases may diffuse rapidly a moist surface on which gases may dissolve and diffuse into and out of cells

Preparatory notes recap What is the surface area to volume ratio of these cubes?

Facts about gas exchange All living organisms take in and get rid of gases (Respiration / Photosynthesis) Some organisms use the body for gas exchange many others use specialised organs The gas exchange takes place by DIFFUSION The amount of cells (volume) determines the amount of gases in/out The rate of diffusion is also proportional to the surface area

To achieve the best diffusion rate, the respiratory area must be… Large Thin Permeable Moist (to allow a medium in which gases can dissolve) The diffusion path must be short

Land organisms Problems: If cells are exposed to air, they’ll dehydrate quickly. Waterproof cover stops diffusion Solutions: Waterproof cover (keratin, chitin, wax) Developing structures specialised in gas exchange: Lungs, tracheae, leaves Aquatic organisms Problems: In Water there is much less dissolved oxygen than in air. Diffusion is much slower in water than in air Solutions: Developing very efficient and large structures to overcome these problems

Application Task Which is the odd one out? surface area to volume ratio? Heat loss? Metabolism?

Take it further: Application Task Human Surface=1.8 m 2 Volume=6.8 dm 3 Ratio= 1: 2.65 dm -1 Earthworm Surface=0.36 dm 2 Volume= dm 3 Ratio=1: 75 dm -1 Earthworms are multicellular, but the gas exchange is still occurring on their body surface….why? How does where they live help gas exchange? Why can humans not do this?

Learning objectives To DESCRIBE the relationship between the size of an organism or structure and its surface area to volume ratio To EXPLAIN the changes to body shape and development of systems in larger organisms as adaptations that facilitate exchange as this ratio reduces? To EXPLAIN the relationship between surface area to volume ratio and metabolic rate?

The Big questions THE BIG QUESTION: How does surface area to volume ratio impact on living organism’s ability to exchange gases and issues arising with gas exchange?

6.1 Gas exchange in Single celled organism and Insects Write me a fact list about gas exchange

Facts about gas exchange All living organisms take in and get rid of gases (Respiration / Photosynthesis) Some organisms use the body for gas exchange many others use specialised organs The gas exchange takes place by DIFFUSION The amount of cells (volume) determines the amount of gases in/out The rate of diffusion is also proportional to the surface area Diffusion surfaces ae usually moist to allow the gases to dissolve

To achieve the best diffusion rate, the respiratory area must be… Large Thin Permeable Moist (to allow a medium in which gases can dissolve) The diffusion path must be short

Land organisms Problems: If cells are exposed to air, they’ll dehydrate quickly. Waterproof cover stops diffusion Solutions: Waterproof cover (keratin, chitin, wax) Developing structures specialised in gas exchange: Lungs, tracheae, leaves Aquatic organisms Problems: In Water there is much less dissolved oxygen than in air. Diffusion is much slower in water than in air Solutions: Developing very efficient and large structures to overcome these problems

Learning objectives To DESCRIBE adaptations of gas exchange surfaces, shown by gas exchange: across the body surface of a single-celled organism in the tracheal system of an insect To EXPLAIN the structural and functional compromises between the opposing needs for efficient gas exchange and the limitation of water loss shown by terrestrial insects

The Big questions THE BIG QUESTIONS: 1.How are SCO and Insects adapted for efficient gas exchange? 2.How do insects compromise between water loss and gas exchange?

Single cells organisms How does the ameoba exchange gases? How can they ensure that a) Carbon Dioxide can leave b) Oxygen can enter?

Earthworms (Annelids) Earthworms are multicellular, but the gas exchange is still occurring on their body surface….why? - large surface area - they live in damp environments How do they carry nutrients/gases around their body? Close circulatory system with a blood pigment

EARTHWORMS have a CLOSED circulatory system The blood contains an oxygen-carrying pigment The major blood vessels are: 1. Ventral blood vessel: distributes the blood to various parts of the body 2. Branches of the ventral blood vessel: Take the blood to all the structures within each segment. 3. Dorsal blood vessel: collects the blood from the body There is a heart and 5 pseudo-hearts to pump the blood around

Insects have an OPEN circulatory system. Insect blood, properly called hemolymph, flows freely through the body cavity and makes direct contact with organs and tissues. The insect circulation system does not carry oxygen, so the blood does not contain red blood cells as ours does. Hemolymph is usually green or yellow. A single blood vessel runs along the dorsal side of the insect. Few little pumps (hearts) push the hemolymph through this vessel (in one direction) to the haemocoele. The hemolymph is then re-absorbed by the dorsal vessel

Label these diagrams

Insects knowledge task Main task Insects are relatively small but they are also very active, so they need to respire ___________. They have a waterproof exoskeleton, which is rigid for protection and covered in ______ to prevent insects drying out. Insects improve their rate of gas exchange by using a network of ________ that carry air directly to the cells. Openings in the insect’s exoskeleton, called __________, lead to a network of tubes called__________, which branch into many smaller ____________. The tracheae and tracheoles are held open by rings of hard ________ (a polysaccharide). The tracheoles penetrate deep into the insects tissues, carrying air directly to every ______. At the ends of the tracheoles oxygen __________ directly into the cells, and carbon dioxide diffuses out, down their concentration gradients. Take it further How are insects adapted for effective gas exchange? How are insects adapted to reduce water loss? Why will we never see giant Insects?

Learning objectives To DESCRIBE adaptations of gas exchange surfaces, shown by gas exchange: across the body surface of a single-celled organism in the tracheal system of an insect To EXPLAIN the structural and functional compromises between the opposing needs for efficient gas exchange and the limitation of water loss shown by terrestrial insects

The Big questions THE BIG QUESTIONS: 1.How are SCO and Insects adapted for efficient gas exchange? 2.How do insects compromise between water loss and gas exchange?