Section 3.1 - Exchange in organisms

What needs to be exchanged by an organism and it's environment?

oxygen, carbon dioxide, nutrients, waste, heat

What factors determine the amount of oxygen needed?

the amount of living cells, and the rate they need to respire

What is surface area to volume ratio?

The amount of surface exposed for a given volume

What is fick's law?

(Surface Area x Concentration Gradient)/Thickness

How does insect gas exchange work?

Insects have a tracheal system

- gases go directly into respiring tissues

- insects have a hard exoskeleton made of chitin

- there are tiny holes in the exoskeleton called spiracles

- these are the openings of tubes called trachea and tracheoles.

- these contain fluid to dissolve gases

What are the organs in plant?

leaves, roots and stems

From where do plants obtain their water?

from the soil through the roots

From where do plants obtain carbon dioxide and oxygen?

from the air, through the stomata into the leaves

What makes up the structure of a leaf?

- waxy cuticle

- upper epidermis

- palisade mesophyll

- spongy mesophyll

- lower epidermis

- stomata

- guard cells

What is the waxy cuticle?

produced by upper epidermis, prevents water loss

What is the upper epidermis?

tightly packed to prevent water loss, see through for photosynthesis in the palisade mesophyll

What is the palisade mesophyll?

made of palisade cells which contain chloroplasts for photosynthesis, large surface area to capture maximal sunlight.

What is the spongey mesophyll?

has air pockets to aid the diffusion/gas exchange of carbon dioxide and oxygen.

What is the lower epidermis?

tightly packed to prevent water loss

What is the stomata?

allows carbon dioxide and oxygen in and out of the leaf

What are guard cells?

open and close the stomata to control gas exchange

How are leaves adapted for gas exchanged?

- stomata and guard cells to control what gases enter and exit the cell

- waxy cuticle to prevent water loss

- spongey mesophyll have air pockets for efficient gas exchange

- leaves are broad and thin to maximise sunlight and diffusion

How are root hair cells adapted?

- large surface area

- one cell thick

Where is transpiration?

xylem

How does the xylem work?

- transports water around the plant through the stem and leaves

- unidirectional

How is xylem tissue adapted?

- made of dead and hollow cells to allow more water through at a time

- thick cell walls strengthened with lignin to withstand

- cells have no end walls

Where does translocation take place?

phloem

How does the phloem work?

- transports glucose and other nutrients dissolved in water

- bidirectional

How is phloem tissue adapted?

- thin walls made of cellulose

- cells have end walls with perforations (sieve tubes)

What is the mass flow theory?

The passive movement of sugars in the phloem from a high concentration (source) to a low concentration (sink)

What is a source and sink?

source is the part of the plant which releases sucrose into the phloem

sink is the part of the plant which removes sucrose from the phloem

What structures are included in human gas exchange?

- trachea

- bronchi

- bronchioles

- alveoli

How is the trachea adapted to gas exchange?

- cartilaginous rings: structural support (prevents it collapsing from air pressure increasing during inhalation)

- mucus traps dirt particles and pathogens (pushed up by cilia)

How are bronchi adapted to gas exchange?

- two divisions off the trachea leading to each lung

- cartilaginous rings: structural support

- also produces mucus

How are bronchioles adapted to gas exchange?

- divisions of the bronchi

- tube-like structures

- muscle lined with epithelial cells, allowing them to constrict and dilate to control the flow of air in and out of alveoli

What are alveoli?

- tiny air sacs at the end of bronchioles

- collagen and elastic fibres between alveoli to provide flexibility to stretch when breathing

How are alveoli adapted for gas exchange?

- large surface area (lined with epithelial cells)

- good blood supply (surrounded by capillaries)

- thin - short diffusion pathway

- moist - dissolve gases

What is the ventilation?

the movement of air in and out of the thoracic cavity

What is the thorax?

chest cavity

- made up of a ribcage which houses the lungs and heart

What happens during ventilation in the thoracic cavity?

- the thoracic cavity expands and contracts allowing for changes in air pressure which is critical for breathing

How does inhalation work?

IT IS ACTIVE

1. the diaphragm and external intercostal muscles contract

2. the thoracic cavity expands as the diaphragm flattens

3. the volume of the thoracic cavity rises and the lung pressure decreases below atmospheric pressure

4. air is drawn into the lungs down a pressure gradient

How does exhalation work?

IT IS PASSIVE

1. the diaphragm and external intercostal muscles relax

2. thoracic cavity contracts and air pressure increases

3. the volume of the thoracic cavity decreases and the pressure rises above atmospheric pressure

4. air moves out the lungs down a pressure gradient

How do you calculate ventilation rate?

tidal volume x respiritory rate

What structures are involved in fish gas exchange?

- gills

- gill filaments

- lamellae

- buccal cavity

- opercular cavity

- operculum

What is the buccal cavity?

the entire mouth cavity of a fish, opened and closed by upper and lower jaws

What is the opercular cavity?

the hollow space between gills and the operculum in a fish

What is the operculum?

A bony flap that covers and protects the gills

What are fish gills?

organs in a fish made of thin tissue allowing the fish to breathe underwater

What are gill filaments?

small feathery structures that are covered in capillaries that extend from the gill arch

What are lamellae?

small protrusions on the gill filaments that help with diffusion

Where do fish get their oxygen from?

the water they swim in

How does the process of gas exchange happen in a fish?

- the fish lowers its jaw to open the buccal cavity to allow water in

- the buccal cavity closes and water is forced over the gill filaments by the pressure difference

- the operculum acts as a valve/pump, allowing water in and out

- blood flows in a different direction to water to maintain a steep conc. gradient so oxygen can diffuse into deoxygenated blood

How are fish adapted to gas exchange?

- lamellae covering gills is only one cell thick and large surface area (easier diffusion)

- counter-current system for conc. gradient

- swimming and gulping quickly, to maintain a good water supply

What is digestion?

process of breaking down food into smaller absorbable molecules

What is the alimentary canal?

the passage by which food passes through the body from mouth to anus

What are the accessory organs involved in digestion?

salivary glands, liver, gallbladder, pancreas

What processes are involved in digestion?

1. ingestion

2. digestion

3. absorption

4. assimilation

5. egestion

What is ingestion?

taking food into the mouth

What are the two types of digestion? Give an example for each.

Physical (e.g. chewing) or Chemical (e.g.enzymes)

What is absorption?

taking digested food into the blood stream

What is assimilation?

absorbed nutrients turning into complex biological molecules

What is egestion?

expelling waste from the body

How do teeth assist digestion?

physically breaking down food so there is more surface area for enzymes to act on

What components make up saliva?

water - dissolves substances

mucus - lubricates food and oesophagus

salts - neutralises food to make it correct pH for stomach

amylase - hydrolyses starch/glycogen to glucose

What happens after food is chewed?

chewed food is formed into a ball/bolus and pushed back to the pharynx where it will leave the mouth and enter the oesophagus

- to stop the food from entering the trachea there is a small flap called the epiglottis which closes over the trachea

How does the stomach assist digestion?

- can store food for several hours

- enzymes are pepsin and lipase

- walls contain gastric pits which secrete gastric juices

- churns every 20 seconds to mix food with gastric juices

- internal surface is folded to allow for distension

How does the pancreas assist digestion?

Exocrine cells of pancreas secrete pancreatic juices which contain digestive enzymes and hydrogen carbonate ions

How does the gallbladder/bile assist digestion?

- bile is secreted into the small intestine (duodenum)

- emulsifies fats and neutralises acidic chyme mixture

- chyme is digested food and gastric juices

How does the small intestine assist digestion?

- muscular tube around 5m long

- 3 parts: duodenum (20cm), jejunum (2m), ileum (3m)

- movement by peristalsis

- takes 3-5 hours to travel through

- enzymes: protease, lipase and amylase

Where is amylase produced and used?

- made in the pancreas and salivary glands

- used in the small intestine for digestion of starch

- used in the mouth for hydrolysis of starch

What is the function of disaccharidases?

break down disaccharides to monosaccharides (e.g. maltose to glucose)

- this makes them small enough to be transported across the plasma membrane of the epithelial cells in the ileum

How are glucose and fructose absorbed?

- glucose is absorbed by co-transport with sodium ions

- fructose is absorbed by facilitated diffusion

What is the function of proteases/peptidases?

breaking down proteins into amino acids by hydrolysing peptide bonds

Where are proteases/peptidases produced and used?

- produced in the pancreas and used in the small intestine

- EXCEPT pepsin, this is made and used in the stomach

Why is pepsin different to other proteases/peptidases?

because it must work at a different pH then other peptidases due to stomach acid having a low pH

What are the 3 types of peptidases?

- endopeptidase

- exopeptidases

- dipeptidases

What does an endopeptidase do?

hydrolyses peptide bonds in the middle of a polypeptide to create more ends

What does an exopeptidase do?

hydrolyses peptide bonds at the ends of a polypeptide

What does a dipeptidase do?

breaks down dipeptides into amino acids

What is the function of lipases?

breaking down lipids by hydrolysing the ester bonds

What are lipids hydrolysed into?

monoglyceride and 2 fatty acids

Where are lipases produced and used?

- made in the pancreas

- used in the small intestine

How is the digestion of lipids facilitated/assisted by bile?

bile emulsifies large lipid droplets into smaller ones, providing a larger surface area for lipase to act on, speeding up the digestion

What is a micelle?

made of bile salts and phospholipids that captures lipid digestion products

What is the function of micelles?

micelles are dynamic, so are constantly breaking and reforming - when they do this they release monoglycerides and fatty acids straight out of the small intestine by simple diffusion across the phospholipid bilayer (like ejecting them out)