exchange surfaces

internal network of tubes supported by strengthened rings to prevent collapse.

smaller dead end tubes leading from tracheae. Extend through the body of the insect direct to respiring tissues providing a short diffusion pathway from air to cells.

pores on surface of insect leading to tracheae, can be opened and closed

Gill filaments stacked on top of each other. Gill lamellae project at right angles to the gill filaments, this increases the surface area of the gills. The gill filaments and lamellae have a good blood supply.

Water is taken in through the mouth of the fish and forced out over the gills. through an opening on the side of the body. Gases are exchanged between the water and the blood vessels in the gills.

In parallel flow the blood and the water flow in the same direction. In countercurrent flow the blood and the water flow in opposite directions.

Rate of gas exchange is increased because counter-current flow maintains a diffusion gradient between the water and the blood over the whole length of the gill.

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Gas exchange occurs by diffusion in the leaves of plants and volumes and types of gases depend on the balance between the rates of photosynthesis and respiration.

Leaf is designed so that cells are close to external air and diffusion occurs in the gas phase. Stomata: found on the underside of the leaf and allow gases to enter. Many stomata so short diffusion pathway to cells Spongy mesophyll: has air spaces so large surface area compared with tissue volume, gases readily come into contact with cells, rapid diffusion

External intercostal muscles contract - internal intercostal muscles relax Ribs pulled upwards and outwards Diaphragm contracts and flattens Volume of thorax increases Pressure in lungs decreases Atmospheric pressure greater than pulmonary pressure - air moves in to lungs

Internal intercostal muscles contract - external intercostal muscles relax Ribs move downwards and inwards Diaphragm relaxes and moves upwards Volume of thorax decreases Pressure in lungs increases Pulmonary pressure greater than atmospheric pressure - air moves out of lungs

Pulmonary ventilation rate is the total volume of air that is moved into the lungs during one minute. Calculated by: tidal volume x breathing rate

Contained within the ribcage for protection and to allow ventilation to occur Trachea - flexible airway from mouth to bronchi, has cartilage for support. Walls made of ciliated epithelium and goblet cells Bronchi - two branches of trachea, similar structure to trachea Bronchioles - branches from bronchi, muscular walls control air flow to alveoli Alveoli - tiny air sacs at the end of bronchioles. made of epithelium with elastic fibres and collagen between alveoli

To allow a large volume of oxygen and carbon dioxide to be exchanged between the blood and the environment. The gases are needed and produced by respiration

Large surface area, thin, movement of internal and environmental medium to maintain diffusion gradient

Single layer of cells for short diffusion pathway Millions of alveoli allowing a very large surface area Good blood supply with many capillaries whose walls are one cell thick for a short diffusion pathway

To hydrolyse large molecules into small ones for absorption from the ileum into the blood

Salivary glands: near mouth. Pass amylase via a duct into the mouth Oesophagus: carries food from mouth to stomach Stomach: muscular sac, produces enzymes to digest protein, stores and digests food Pancreas: gland secreting pancreatic juice containing protease, amylase and lipase Ileum: long muscular tube, walls and glands secrete enzymes. villi and microvilli to increase surface area Large intestine: absorbs water Rectum: stores faeces and egests them via the anus

Physical digestion: large pieces of food to small pieces by chewing and churning of stomach - increases SA for enzyme action Chemical: Enzymes hydrolyse large insoluble molecules into small soluble molecules

Saliva contains amylase which hydrolyses starch to maltose and mineral salts to maintain pH7 Stomach denatures amylase from mouth Pancreas secretes pancreatic juice containing amylase and alkaline salts to neutralise stomach acid Ileum produces the membrane bound disaccharidase maltase which hydrolyses maltose to alpha glucose Additional disaccharidases: lactase and sucrase

Lipases hydrolyse triglycerides (lipids) into monoglycerides and fatty acids Bile salts emulsify lipids to increase the surface area for enzyme action

Endopeptidases: hydrolyse peptide bonds between amino acids in the middle of a polypeptide producing shorter polypeptides Exopeptidases: hydrolyse peptide bonds on the ends of the polypeptide producing single amino acids and dipeptides Dipeptidases: membrane bound, hydrolyse dipeptides into single amino acids

Micelles (containing monoglycerides, bile salts and fatty acids) come into contact with epithelial cells lining ileum and break open. Monoglycerides and fatty acids diffuse into epithelial cell through phospholipid bilayer (they are lipid soluble). Monoglycerides and fatty acids reform triglycerides in the endoplasmic reticulum. Chylomicrons (triglycerides, lipoproteins, cholesterol) formed in the golgi apparatus Chylomicrons leave cell by exocytosis into the lacteal (lymphatic capillary) in the villus Chylomicrons move from the lymphatic vessels into the blood stream Triglycerides hydrolysed by enzymes in endothelial cells of blood capillaries from where they diffuse into cells