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define metabolism

All the chemical reactions/processes that take place
in the cells/body
• 2 main types:
o Building/synthesising
o Using smaller molecules to build/make larger
o E.g. protein synthesis

o Breaking down larger molecules into simpler
o E.g. digestion (releases energy)

• This is done using enzymes


what are enzymes (structure, role)

organic catalysts: speed up rate of reaction and lower activation energy

specific proteins

Have an activation site: specific site that will only combine with specific molecules (substrate)

Substrate: molecule on which enzyme acts upon

lock and key model:
- enzymes are specific & fit together perfectly, like a lock
and key
- enzyme is like a specific key shaped to fit the lock
(substrate) and only the correct enzyme can connect
with the substrate


what is cell respiration

Complex chemical reactions that take place in the cells cytoplasm and mitochondria (cristae)

Process of converting glucose to a usable form of energy (ATP) + heat


Explain what happens during the stage of glycolisis

doesn't require oxygen or energy

occurs in cytoplasm

breaks down 1 glucose molecule into 2 pyruvate molecules

produces 2 ATP


Explain what happens during the stage of Anaerobic respiration

occurs when oxygen is not available e.g. during exercise

occurs in cytoplasm

breaks down 2 pyruvate molecules into 2 lactic acid molecules produced through fermentation

energy from glycolysis converts 2 ADP into 2 ATP


Explain what happens during the stage of Aerobic respiration

occurs in mitochondria

step 1:
pyruvate molecules enter mitochondria
pyruvate is converted into acetyl CoA (1 carbon dioxide is removed & remaining 2-carbon structure joins to coenzyme A)

step 2:
acetyl CoA enters Krebs cycle
carbon atoms in acetyl CoA produces carbon dioxide and hydrogen ions
2 ATP produced

step 3:
uses oxygen
enters electron transport system: electrons are passed along electron transfer chain, hydrogen ions eventually collide with carbon dioxide and water is produced
produces 24 ATP

26 - 34 ATP produced **theoretical maximum


explain the 7 factors affecting enzyme activity

1. concentration of enzyme: higher concentration of enzymes, faster rate of reaction because more enzymes present

2. concentration of substrate: increasing substrate concentration increases rate of reaction because more substrates contact enzymes

3. temperature: rate of reaction increases as temperature increases within optimum range (30 - 40˚) or enzyme denatures

4. pH: each enzyme has an optimum pH where it'll work most effectively

5. products must be continually removed: or rate of reaction will slow because it'll be more difficult for substrates to contact enzymes

6. presents of cofactors of coenzymes: ions of non-proteins molecules that catalyse reactions.
cofactors: change shape of active site so enzyme can contact substrate
coenzyme: non-protein organic molecule e.g. vitamins

6. enzyme inhibitors: slow or stop reactions, controls the amount of products produced


explain what 'nutrients' is

Substances found in food required by cells for growth, repair & cell functioning

Food contains large complex molecule too big to enter and be used in cells

food must be digested to access nutrients

Organic nutrients/compounds: contain carbon e.g. carbohydrates, protein, lipids

Inorganic nutrients/compounds: vitamin, minerals, water


what are the functions of the digestive system

1. Ingestion: physical process of taking food into the

2. Movement: muscle contractions move the molecules
along the alimentary canal

3. Mechanical digestion: break up of larger particles
into smaller particles

4. Chemical digestion: break down of molecules from
complex particles into its simplest form

5. Absorption: Simplest form of nutrients move from
the small intestine into the bloodstream

6. Elimination: formation of faeces to remove unwanted
materials from the body


describe the alimentary canal

• Tube that connects mouth to anus

• All structures that nutrients travel through

• E.g. mouth, pharynx, oesophagus, stomach, small
intestine, large intestine, anus


what are accessory organs

• Structures that are outside the alimentary canal

• Play a role in digesting the nutrients

• E.g. salivary glands, liver, pancreas, gall bladder


what are the 2 types of digestion

1. Mechanical: physical process of breaking up larger
particles into smaller ones

2. Chemical: chemical process of breaking up complex
molecules/nutrients into its simplest form e.g.


explain digestion in the mouth

pHl neutral to slightly acidic (6 - 7)

mechanical digestion:
mastication: action of the jaw and teeth breaking up food into smaller piece

4 incisors: chisel shaped, biting & cutting
2 canines: tearing food
4 premolars: crushing & grinding food
6 molars: broad crowns for crushing & grinding food

tongue pushes bolus toward pharynx for swallowing

chemical digestion:
Salivary amylase is secreted by 3 pairs of salivary glands

Breaks down complex starch into polysaccharides


describe digestion in the stomach

pH: highly acidic (2 - 3)

mechanical digestion:
Waves of muscular contraction churns food to create a thick, soupy liquid called chyme

chemical digestion:
Pepsin is secreted from gastric glands

Hydrochloric acid breaks down bacteria and provides optimum pH for pepsinogen

When pepsinogen comes into contact with HCl it is converted into pepsin (active)

Pepsin breaks down complex proteins into polypeptides


describe digestion in the duodenum

pH: alkaline (7-8)

(no mechanical digestion)

chemical digestion:
**liver produces bile: bile salts neutralise stomach acid & emulsify fats

Pancreas produces pancreatic juice secreted pancreatic duct:
• Pancreatic amylase: breaks down polysaccharides
into disaccharide
• Trypsin: breaks down polypeptides into dipeptides
• Pancreatic lipase: breaks down fats into fatty acids
and glycerol
• Ribonuclease and deoxyribonuclease: breaks down


describe digestion in the ileum and jejunum

pH: slightly alkaline (7-8)

(no mechanical digestion)

chemical digestion:
**most food absorption occurs here
**liver produces bile: bile salts neutralise stomach acid & emulsify fats
**6-7 m long

Intestinal glands produce:
• Intestinal amylase: breaks down disaccharides into
• Intestinal peptidase: breaks down dipeptides into
amino acids
• Intestinal lipase: breaks down fat into fatty acids and


describe digestion in the large intestine

• 1.5m long
• No digestion or enzymes: water is absorbed
• 18 – 24 hours
• Glands secrete mucous
• Bacteria breaks down any remaining organic
• Vitamins produced by bacteria are also


explain the process of defecation

Removal of metabolic waste producesdby chemical
activity of the cells

Referred to as elimination

Faeces contain:
- Water
- Undigested food material
- Bacteria
- Bile pigments
- Remains of cells broken away from alimentary canal


explain absorption in the small intestine

Occurs through Villi:
- small, finger-like projections from the wall of the small

- Microvilli cover each villus to increase surface area for

- Villi are one cell thick and 1 mm long

- Villi are constantly moving to come into contact with the

- Inside each Villus is a lymph capillary (lacteal)
surrounded by a network of blood capillaries

- Absorption occurs through simple diffusion & active


explain different nutrients absorption into the bloodstream

Fatty acids, glycerol & fat soluble vitamins:
- Enter the lacteal via simple diffusion
- In the villi cells the fatty acids and glycerol combine to
form tiny fat droplets that then enter the lacteals

Amino Acids
- Absorbed into blood capillary network by simple

Simple Sugars (e.g. glucose)
- Absorbed into blood capillary network by active

Water and water soluble vitamins:
- Enter blood capillary network via simple diffusion


define excretion

Process of removing all metabolic waste products from the body


give examples of metabolic waste

Heat: remove through skin

Carbon dioxide: removed through lungs

Salts: skin

Lactic acids: kidneys

Bile pigments: alimentary canal

Urea: kidneys

Water: lungs and skin


explain the function of skin in the excretory system

Provide protective covering over surface of the body

Regulate body temperature

Plays important role in excretion
- Sweat gland are located in lower layers of skin
- A duct carries the sweat to a hair follicle or skin surface
where it opens at a pore
- Cell surrounding the glands are able to contract and
squeeze the sweat to the surface
- Glands secrete about 500mL water per day
- Dissolved in it are:
o Sodium chloride
o Urea
o Lactic acid
o Some drugs e.g. salicylic acid


explain the process of deamination

occurs in the liver (located in upper abdominal cavity)

Metabolic process that breaks down excess protein so it can be excreted

Part 1:
- Excess proteins are broken down in the liver into
amino acids
- The NH2 amino group is removed from the amino acid
- The NH2 group is converted into ammonia

Amino acid + oxygen ------enzymes----> carbohydrate + ammonia

Part 2:
- The remains of the amino acid (carbon - hydrogen structure) is converted into a carbohydrate which is used to release energy, CO2 and water
- Ammonia is highly toxic to cells so it is quickly converted into the less toxic urea
- Urea is excreted in the form of urine, small amounts are lost in in sweat

Energy + carbon dioxide + ammonia -----> urea + water


Explain the kidneys in the excretory system

Primary excretion organs

Each kidney is about 11cm long

Surrounded by fibrous connective tissue called the capsule

Three layers:
Cortex: outer layer
Medulla: middle layer
Renal pelvis: inner layer


what are nephrons

• Nephron: functional unit of the kidney, its where
urine is formed

• Kidneys are composes of a large number of

• About 2 million nephrons in each kidney


explain the structure of nephrons

Each nephron consist of a renal corpuscle and a renal tube, located in renal pyramids

Renal corpuscle:
- Consists of the glomerulus and glomerular capsule: expanded side of the nephron

Renal tube:
- Leads away from the glomerular capsule
- About 5 cm long
- Begins with a winding section called the proximal
convoluted tubule
- Beyond this each tubule has a straight portion before it
forms the loop of Henle
- Then the tubule becomes coiled again (second coiled
section is called the distal convoluted tube)
- Distal convoluted tube joins a collecting duct that opens up into the renal pelvis (which channels fluid from collecting ducts into the ureter)


Explain the function of nephrons

Responsible for removing waste from blood and regulating blood composition:

- Blood enters the kidney through the renal
- Renal arteries divide into smaller arteries and
- Each renal corpuscle is supplied with an afferent
arteriole which forms a knot of capillaries called
the glomerulus
- Capillaries unite to form the efferent arteriole
which passes out of the renal corpuscle
- After leaving the renal corpuscle the efferent
arteriole breaks up into a second capillary
network (peritubular capillaries)
- These surround the proximal and distal
convoluted tubules, the loop of Henle and the
connecting duct
- Blood drains away from the peritubular
capillaries and leaves the kidney the renal vein


What are the differences between the afferent and efferent arterioles

1. Afferent arteriole has a wider diameter than the
efferent arteriole

2. Afferent arteriole carries blood into the nephron,
efferent carries blood away


what are the 3 processes involved in urine formation

glomerular filtration

selective re-absorption

tubula secretion