Organisms exchange with the environment

Question 1

Describe the structure of
fish gills

Answer 1

-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

Question 2

Describe how a fish
exchanges gases

Answer 2

• 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.

Question 3

Explain the difference
between parallel flow and
counter-current flow

Answer 3

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

Question 4

Explain how
counter-current flow
increases the rate of gas
exchange

Answer 4

-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.

Question 5

Describe the relationship between the size of an organism or structure and its surface area to volume ratio

Answer 5

The larger an organism the smaller its surface area to volume ratio.

Question 6

Describe how larger organisms increase their surface area to volume ratio

Answer 6

Larger organisms require specific exchange surfaces with large surface areas to obtain the substances they need.

Question 7

Explain how surfaces are specially adapted to facilitate exchange

Answer 7

• large surface area relative to the volume of the organism to increase the rate of exchange
• thin so diffusion distance is short and materials can cross exchange surface rapidly
• selectively permeable to allow materials to cross
• movement of the environmental medium to maintain diffusion gradient
• transport system to ensure movement of internal medium to maintain diffusion gradient”

Question 8

Describe the relationship between SA:vol and metabolic rate

Answer 8

Organisms with a high metabolic rate exchange more materials and therefore need a larger surface area to volume ratio

Question 9

Describe how single celled organisms exchange gases

Answer 9

Single celled organisms are small and therefore have a large surface area to volume ration. This is sufficient to exchange the substances required

Question 10

Describe how an insect exchanges gases

Answer 10

-Spiracles - pores on surface of insect leading to tracheae, can be opened and closed
-Tracheae - internal network of tubes supported by strengthened rings to prevent collapse.
-Tracheoles - 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.

Question 11

Explain how insects exchange gases

Answer 11

1. Diffusion gradient - respiration in cells uses oxygen, concentration falls in ends of tracheoles, produces a diffusion gradient causing oxygen to diffuse down from the atmosphere. The opposite applies to carbon dioxide
2. Mass transport - contraction of muscles squeezes trachea and enables mass movement of air
3. Water in tracheoles - intense activity causes muscle cells to respire anaerobically, producing soluble lactic acid which lowers water potential of muscle cells, water moves into cells from tracheoles by osmosis, lowering volume in tracheoles, drawing air further in and allowing it to diffuse in gas phase rather than liquid which is more rapid.”

Question 12

Describe how plants exchange gases

Answer 12

-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.

Question 13

Explain the adaptations of leaves for efficient gas exchange

Answer 13

-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

Question 14

Explain how xerophytic plants balance the need to exchange gases with the need to conserve water

Answer 14

Plants have a large SA for photosynthesis.
To reduce water loss by evaporation:
- waterproof covering (waxy cuticle) on leaves
- Close stomata
- reduced SA:vol eg pine needles
The following adaptations trap air with high water potential to reduce water potential gradient
- rolled leaves
- hairy leaves
- stomata in pits”

Question 15

Explain how terrestrial insects balance the need to exchange gases with the need to conserve water

Answer 15

Exchange surface has large surface area but the insect has:
- small SA:vol
- waterproof covering - chitin and a waterproof cuticle
- spiracles can be closed to reduce water loss

Question 16

Describe the structure of the human gas exchange system

Answer 16

“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”

Question 17

Explain the functions of the human gas exchange system

Answer 17

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

Question 18

Describe the sequence of events that lead to inspiration and expiration

Answer 18

INSPIRATION
-External intercostal muscles contract - internal intercostal muscles relax
-Ribs pulled upwards and outwards
-Diaphragm contracts and flattens

EXPIRATION
-Internal intercostal muscles contract - external intercostal muscles relax
-Ribs move downwards and inwards
-Diaphragm relaxes and moves upwards

Question 19

Explain how and why air is moved in the lungs during inspiration and expiration

Answer 19

INSPIRATION
-Volume of thorax increases
-Pressure in lungs decreases
-Atmospheric pressure greater than pulmonary pressure - air moves in to lungs

EXPIRATION
-Volume of thorax decreases
-Pressure in lungs increases
-Pulmonary pressure greater than atmospheric pressure - air moves out of lungs

Question 20

Explain what is meant by pulmonary ventilation and how it is calculated

Answer 20

-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

Question 21

Describe the features of the gas exchange surface in humans

Answer 21

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

Question 22

Explain how the alveolar epithelium is adapted to maximise gas exchange

Answer 22

-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

Question 23

Describe the purpose of digestion

Answer 23

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

Question 24

Describe structure and function of organs of the digestive system

Answer 24

-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

Question 25

Explain how food is physically and chemically digested

Answer 25

-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

Question 26

Describe how lipids are digested

Answer 26

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

Question 27

Describe how carbohydrates are digested

Answer 27

-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

Question 28

Describe how proteins are digested

Answer 28

-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

Question 29

Describe the structure of the ileum

Answer 29

Folded, villi containing capillaries and microvilli

Question 30

Explain how the ileum is adapted for absorption

Answer 30

-Villi - finger-like projections. -Many blood capillaries, maintain diffusion gradient. Increase SA for diffusion. -Thin walls so short diffusion pathway.
-Contain muscle so can move, mixes contents of ileum and maintains diffusion gradient.
-Epithelial cells of villi have microvilli further increasing SA

Question 31

Explain how monosaccharides and amino acids are absorbed

Answer 31

-These products of digestion are absorbed by diffusion in the first instance and when the concentration becomes unfavourable by co-transport

Question 32

Explain how triglycerides are absorbed

Answer 32

-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