year 11 biology

requirements of a gas exchange surface

moist

thin and permeable

high SA/V ratio

concentration gradient

why must a gas exchange surface be moist?

because gases dissolve in water to diffuse from one side of the membrane to the other

why must a gas exchange surface be thin and permeable?

so gas molecules can cross it quickly and easily

why must a gas exchange surface have a high SA/V ratio?

to supply gas requirements (O2) and remove gas wastes (CO2) at a fast enough rate for survival

why must a gas exchange surface have a concentration gradient?

allows passive diffusion of gases to where they are needed (save energy in transport)

path of air in mammal respiratory system

outside -> nose -> pharynx -> epiglottis -> larynx -> trachea -> bronchi -> bronchioles -> alveoli

(and then back out)

alveoli

air sacs at the ends of bronchioles

where does gas exchange occur in lungs?

between alveoli and capillaries:

separates internal from external environment

how do our lungs achieve moistness?

they are internal to hide them from outside air where they would dry out

how do our lungs achieve high SA/V ratio?

lots of branching from bronchi to bronchioles to alveoli, which are small and numerous for high SA

how small and numerous are alveoli?

50μm (micrometres)

lungs have ~300 million

how do our lungs achieve thin and permeable surfaces?

walls of alveoli are only 1 cell thick (epithelial cell layer) and are are wrapped in capillary network - forms a thin membrane between

how do our lungs achieve a concentration gradient?

capillaries bring deoxygenated blood to alveoli and take oxygenated blood away

where does oxygen move during gas exchange?

diffuses from alveoli (high in O2) to capillaries (low in O2)

simple diffusion

passive movement of a substance down its concentration gradient: from high to low concentration

where does carbon dioxide move during gas exchange?

diffuses from capillaries (high in CO2) to alveoli (low in CO2)

what animals do not need a complex respiratory system?

small ones with a high SA/V ratio

that live in a moist environment

(gas exchange requirements can be met through skin, etc.)

red blood cells

has haemoglobin (protein with iron) that gently binds to oxygen for transport from lungs to cells

what does blood do?

transports O2 and nutrients to body cells

carries away CO2 and metabolic wastes

3 types of blood vessels

arteries, veins, capillaries

arteries

carry blood away from the heart:

muscular and thick

veins

carry blood to the heart:

muscular and thick (but less so than arteries)

capillaries

carry blood between arteries, cells, and veins:

small and numerous

aorta

main artery of body

(most muscular blood vessel: needs highest pressure to go to whole body from heart)

vena cava

main vein of body

(has valves to stop blood from flowing backwards from lower pressure - blood has travelled further since heart)

which side of the heart is more muscular?

left side: needs to pump blood all the way around the body

(right side only pumps it to lungs)

atrium

one of two upper chambers of the heart:

receives blood coming into heart

ventricle

one of two lower chambers of the heart:

pumps blood out of heart

4 chambers of the heart

right atrium, right ventricle, left atrium, left ventricle

where does oxygenated blood travel from the lungs?

from lung capillaries -> pulmonary vein -> left atrium -> left ventricle -> aorta -> capillaries -> capillaries at body cells

where does deoxygenated blood travel away body cells?

from capillaries at body cells -> vena cava -> right atrium -> right ventricle -> pulmonary artery -> lung capillaries

4 macronutrients (biological molecules)

carbohydrates, lipids, proteins, (nucleic acids)

micronutrients

vitamins (A, B, C, etc.)

minerals (ions: potassium, iron, calcium, sodium, etc.)

carbohydrates components

monosaccharides: e.g. glucose, fructose

(also disaccharides: e.g. sucrose)

carbohydrates examples

polysaccharides:

cellulose (plant cell walls),

starch (plant energy storage),

glycogen (animal energy storage - muscles)

lipids components

glycerol backbone and fatty acids

proteins components

made of amino acids (20 different ones):

form chains called polypeptides

saturated lipids

fatty acids with all single bonds with hydrogen

unsaturated lipids

fatty acids with one or more double bonds

lipids examples

triglycerides (energy storage),

phospholipid (cell membranes),

steroids (hormones)

proteins examples

enzymes (chemical reactions),

antibodies (immune system),

endorphins (emotions)

purpose of digestive system

to break down food into building blocks to be used by cells, and dispose of waste from process

mechanical digestion

physical breakdown of food into smaller pieces

(to increase SA for chemical digestion)

e.g. teeth, muscles

chemical digestion

chemically breaking bonds (through use of enzymes) for smaller molecules

e.g. saliva, stomach acid, etc.

absorption

building blocks entering internal environment (by crossing membranes into bloodstream)

e.g. capillaries in small intestine

path of food in digestive system

mouth, oesophagus, stomach, small intestine, large intestine, rectum, anus

bolus

food after it has been chewed and mixed with saliva in mouth

chyme

mixture of enzymes and partially-digested food from stomach

mouth

start of digestive system:

mechanical digestion: breaking down food with teeth,

chemical digestion: starch by salivary amylase,

make food into bolus to go down oesophagus

salivary glands

glands in the mouth that secrete saliva: contains amylase

oesophagus

long tube connecting mouth to stomach:

peristalsis: wave-like muscle contraction,

bolus is passed down to stomach

stomach

large muscular sac:

bolus enters through cardiac sphincter

mechanical digestion: muscles

chemical digestion: mixed with acidic gastric juices - HCl and pepsin from stomach lining

chyme released to small intestine though pyloric sphincter

chief cells and parietal cells

release enzymes into stomach (for gastric juices) from lining:

chief cells - have pepsin, activates through denaturing in acidic pH

parietal cells - have hydrochloric acid (HCl) that activates the pepsin inside the stomach and kills microorganisms

sphincters

circular muscles that contract to close off a tube:

cardiac sphincter - bottom of oesophagus, prevents back flow from stomach

pyloric sphincter - top of small intestine, controls release from stomach

small intestine - duodenum

first part of the small intestine:

pancreatic juice and bile secreted in from pancreas and liver

further digestion of macromolecules in chyme into building blocks

liver

produces bile (for small intestine):

breaks down hydrophobic fats into fatty acids etc. for absorption

gallbladder

stores bile before release into small intestine

pancreas

produces pancreatic juices (for small intestine):

amylase - breaks down carbohydrates

protease - breaks down proteins

lipase - breaks down lipids

small intestine - jejunum and ileum

latter parts of the small intestine:

chyme passes through villi and microvilli;

absorb nutrients (building blocks of macromolecules: amino acids, etc.) into bloodstream

villi / microvilli

long fingerlike projections from interior walls of small intestine,

filled with capillaries for absorption of nutrients

(microvilli are projections from projections)

to maximise SA/V ratio

large intestine

completes digestion:

remaining water, salt, minerals absorbed from chyme,

faeces moved to rectum through peristalsis

appendix

attached to the large intestine:

stores useful bacteria

rectum/anus

rectum stores faeces until it is expelled from anus

enzyme

protein that is a biological catalyst:

controls and speeds up a chemical reaction

how does an enzyme work?

binds to substrate molecule(s),

synthesises or breaks them down,

releases products(s)

active site

part of enzyme where the substrate binds:

specifically shaped to fit perfectly to substrate molecule (lock and key model)

why are there so many different types of enzymes?

each type will only catalyse a specific reaction,

can only bind to a specific substrate molecule

can an enzyme be reused?

can be reused:

does not get used up in a reaction (catalyst)

denature

when an enzyme changes shape and cannot catalyse reaction: active site doesn't fit to substrate anymore

factors affecting enzymes

temperature, pH, substrate concentration

how does temperature affect enzyme activity?

low temperatures lead to less particle collisions (collision theory)

high temperatures denature enzymes

how does pH affect enzyme activity?

low (too acidic) or high (too basic) pH denatures enzymes

how does substrate concentration affect enzyme activity?

low concentration leads to less particle collisions (collision theory)

higher concentration leads to more particle collisions (until all enzymes are occupied at all times)

photosynthesis equation

6CO2 + 6H2O + light energy --> C6H12O6 + 6O2

gas exchange in leaves

CO2 diffuses in through stomata and O2 (and H2O) diffuses out

how do leaves obtain H2O for photosynthesis?

roots absorb H2O from soil (yay gravity)

how do leaves maximise SA/V ratio for gas exchange?

large flat structure, air spaces inside leaves for fast diffusion

stomata

the small openings on the undersides of leaves through which gas exchange occurs, flanked by crescent-shaped guard cells

how do guard cells open/close the stomata?

stomata open when guard cells take up water and become turgid, they close when guard cells lose water and become flaccid

when does the stomata open/close?

open in moist conditions, close in drier conditions:

conserves water, because moist conditions means less water vapour lost to environment when open

structure of a leaf (top to bottom)

cuticle, upper epidermis, palisade mesophyll, spongy mesophyll and vascular bundles, lower epidermis, stomata

cuticle

thin transparent wax layer on top of a leaf (to reduce water loss)

upper and lower epidermis

surface layer of cells

mesophyll cells

cells that contain chloroplasts and host photosynthesis

spongy mesophyll

loosely arranged, irregular-shaped mesophyll cells with spaces between for gas movement

palisade mesophyll

densely packed, elongated mesophyll cells with many chloroplasts (for maximum light absorption near the top of the leaf)

vascular tissue

series of tubes within plants consisting of xylem and phloem

transport in xylem

transports water and minerals upwards (from roots to leaves)

what is xylem made of?

non-living cells: tracheids and vessel elements

processes involved in water transport through xylem

transpiration,

osmosis and diffusion,

cohesion,

adhesion

transpiration

evaporation of water from the leaves of a plant, out of stomata

osmosis and diffusion in xylem

water and dissolved minerals diffuse into roots and up plant from soil (moving from high to low pressure):

transpiration keeps the water pressure lower at the leaves to continue upward water flow

cohesion in xylem

attraction of water molecules to each other

(polar with hydrogen bonding forces):

keeps them moving together in a chain

adhesion in xylem

attraction of water molecules to the xylem walls (hydrophilic):

allows upward transport against gravity

transport in phloem

transports sugars from the source to sink in different directions

source

leaves: produces sugars and releases them into phloem

sink

roots etc.: receives sugars from phloem to store and use for growth

phloem loading

active transport of sugars from source cells into phloem

what does phloem loading do?

high concentration of sugar in phloem causes diffusion of water into phloem from xylem (osmosis):

-> causes high turgor pressure in phloem at source compared to at sink

-> leads to passive transport of solution from source to sink

what is phloem made of?

living cells: sieve tube cells and companion cells