Bioenergetics

3.2 IGCSE BIOLOGY

Photosynthesis equation

6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂

Carbon dioxide + water + light energy → glucose + oxygen

During photosynthesis

light is absorbed by chlorophyll, which is found in the chloroplast, light is used to convert carbon dioxide (from the air) and water (from the soli) into sugar (glucose) oxygen is released as a by-product

Factors that affecting the rate of photosynthesis

Temperature: As the temperature increases so does the rate of reaction- this is because the particles have greater energy so more successful collisions occur. Otherwise the enzymes denature (change shape).

Light intensity: As the light intensity increases so does the rate of photosynthesis.The rate of reaction begins to level off because another factor is limiting the reaction e.g. carbon dioxide or temperature.This means that further increases in light have no effect

Concentration of Carbon Dioxide: As the carbon dioxide concentration increases so does the rate of photosynthesis. The rate of reaction begins to level off because another factor is limiting the reaction

Glucose can be used to be converted to: 

• Sucrose → Transported via phloem to other organs

• Starch → Energy store (in organs, storage organs, seeds)

• Cellulose → Cell wall synthesis

• Fats/oils → Energy store in seeds

• Proteins → (Requires nitrogen) Used for growth, enzymes, DNA synthesis, and energy storage in seeds

The hearts structure

• The upper chambers are called atria (right and left) — they receive blood.

• The lower chambers are ventricles (right and left) — they pump blood out.

• The right side of the heart deals with deoxygenated blood (low in oxygen).

• The left side deals with oxygenated blood (rich in oxygen).

• The septum is a thick wall dividing the right and left sides to prevent mixing.

• The heart is surrounded by blood vessels:

  • Vena cava – brings blood from the body to the heart.

  • Pulmonary artery – carries blood to the lungs.

  • Pulmonary veins – bring blood back from the lungs.

  • Aorta – carries oxygenated blood from the heart to the body.

• Tendons (heart strings) hold the inner flaps in place, stopping them from turning inside out.

Function of the heart

• The heart’s main job is to pump blood throughout the body.

• It delivers oxygen and nutrients to body cells and removes carbon dioxide and waste.

• It works as a double pump:

  • The right side sends blood to the lungs to pick up oxygen.

  • The left side sends blood to the rest of the body to supply oxygen.

• This continuous pumping keeps all organs supplied with what they need to function properly.

Blood flow pathway

• From the body → blood enters the right atrium through the vena cava.

• Blood moves down into the right ventricle.

• The right ventricle pumps blood through the pulmonary artery to the lungs.

• In the lungs, blood releases carbon dioxide and collects oxygen.

• Oxygen-rich blood returns to the left atrium through the pulmonary veins.

• It moves down into the left ventricle.

• The left ventricle pumps oxygenated blood out through the aorta to the body.

Circulation types 

Pulmonary Circulation:

• Moves blood between the heart and lungs.

• Function: To exchange gases — blood loses carbon dioxide and gains oxygen.

Systemic Circulation:

• Moves blood between the heart and the rest of the body.

• Function: To deliver oxygen and nutrients to tissues and collect waste for removal.

Key supporting parts of the heart

Septum:

• A muscular wall separating the left and right sides of the heart.

• Prevents oxygenated and deoxygenated blood from mixing.

Tendons:

• Thin, strong cords inside the heart.

• Hold the inner flaps in position during pumping, ensuring blood moves in the correct direction.

Structure of Arteries and Veins

• Arteries: Thick, muscular, and elastic walls to withstand high pressure and carry blood away from the heart.

• Veins: Thinner walls and wider lumen, carrying blood back to the heart at lower pressure; often contain inner flaps to prevent backflow.

What is blood made of and what is its function?

• Blood is a tissue consisting of plasma with red blood cells, white blood cells, and platelets suspended in it.

• It transports substances to and from body tissues through capillaries, where exchange occurs.

What does blood plasma transport?

• Carbon dioxide from organs to the lungs

• Soluble products of digestion from the small intestine to other organs

• Urea from the liver to the kidneys

What are the main features and functions of red blood cells?

• No nucleus

• Contain haemoglobin, a red pigment that binds to oxygen

• Transport oxygen from the lungs to body organs (as oxyhaemoglobin)

• In organs, oxyhaemoglobin splits into haemoglobin and oxygen

What do white blood cells do?

• Have a nucleus

• Form part of the body’s defence system against microorganisms

What are platelets and what role do they play?

• Small fragments of cells with no nucleus

• Help blood clot at the site of a wound

How does blood clotting work?

• Series of enzyme-controlled reactions change fibrinogen into fibrin, forming a mesh of fibres that traps blood cells to make a clot

What are antigens?

• Proteins on the surface of cells that help identify them to the immune system

How does the immune system work?

anti bodies engulf a pathogen [eg bacteria], ingest it making a vacuole within the cell.

The pathogens are then destroyed by digestion, using enzymes. This process is

called phagocytosis.

they have immunological memory, meaning that when the same threat returns it acts faster and stronger

Lymphocytes (type of white blood cell that are crucial to the immune system)

Lymphocytes make chemicals called antibodies. Antibodies destroy pathogens by:

•​Making them stick together [so that they can be destroyed by phagocytes].

•​Destroying bacterial cells by bursting their cell walls.

•​Produce antitoxins which destroy toxins produced by bacteria.

•​There are specific antibodies for each pathogen.

What is double circulation in humans

• Blood passes through the heart twice per circuit.

• The right side pumps blood to the lungs (pulmonary circulation).

• The left side pumps blood to the rest of the body (systemic circulation).

what are the advantages of a double circulation 

• Low pressure circulation to the lungs → prevents damage to capillaries.

• High pressure circulation to the rest of the body → ensures blood flows faster over longer distances.

• Prevents mixing of oxygenated and deoxygenated blood.

what causes a pulse 

• Pulse is caused by an increase in blood pressure pushing against the elastic walls of arteries each time the heart beats.

How does exercise effect the pulse 

1. increase in energy demand in muscles:

   • For muscle contraction.

   • Increases aerobic respiration in muscles.

2. Increased blood flow to muscles to:

   • Supply more oxygen and glucose for aerobic respiration.

The digestive system

starch (a carbohydrate), proteins and fats are insoluble. they are broken into soluble substances so that they can be absorbed into the bloodstream in the wall of the small intestine.

In the large intestine much of the water mixed with food is absorbed into the bloodstream.

The indigestible food which remains and makes up the bulk of the faeces. Faeces leave the body through the anus. 

What are enzymes

Enzymes are large proteins that act as biological catalysts. They help in the digestive process to speed up the breakdown of large molecules to small molecules for absorption into the bloodstream. 

The active site of an enzyme

•​Enzymes are specific in their action because of their active sites

•​The shape and structure of the active site is complimentary to the substrate.

•​This allows enzymes to catalyse reactions involving specific substrates only.

Factors effecting enzyme action

•​Temperature.

•​pH.

•​Substrate concentration.

•​Enzyme concentration.

Enzymes are denatured at extreme temperatures and pH

Digestion in the mouth 

​Teeth: mechanically digest food – cutting, chewing, grinding and mixing with

saliva

•​Salivary glands – secrete the enzyme amylase which catalyses the break down of starch to sugars

Digestion in the stomach

​Pepsin / PROTEASE: breaks down proteins to polypeptides.

•​ Functions of the hydrochloric acid

•​ Creates low pH required for pepsin [optimum pH=2].

•​ Denatures enzymes in harmful microorganisms in food.

•​ Destroys bacteria in food.

Digestion in the small intestine 

Duodenum: receives pancreatic juice from pancreas [via pancreatic duct] and

bile from the gall bladder [via the bile duct].

•​ Pancreatic juice:

•​ Amylase: breaks down starch to maltose

•​ Trypsin: breaks down proteins to polypeptides

•​ Lipase: breaks down fats to fatty acid and glycerol

•​ Bile:

•​ A greenish-yellow, alkaline, watery liquid – helps to neutralise the acidic

mixture of food and gastric juices entering the duodenum from the

stomach and to provide a suitable pH for enzyme action.

•​ Bile salts emulsify fats [mechanical digestion]. This increases the surface

area for the chemical digestion of fat to fatty acids and glycerol by

lipase.

Absorption in the small intestines 

VILLI are tiny projections [1mm in length] of the inner wall of all parts of the

small intestine. These increase the surface area for absorption.

•​Epithelial cells covering the villi secrete enzymes which do not enter the lumen

of the SI, but stay close to the epithelial cells:

•​ Carbohydrase: sugars to glucose.

•​ Proteases: polypeptides to amino acids.

•​ Lipase: fats to fatty acid and glycerol​

•​ Glucose, amino acids, fatty acids and glycerol are small enough to be passed

through the wall of the SI into the blood – Absorption.​

•​ Water is absorbed in both the small intestine and the colon, but most

absorption of water happens in the small intestine.

Absorption in the large intestine:

•​Colon: water and salts absorbed.

•​Rectum: undigested food [roughage/ fibre + bacteria + dead cells from

alimentary canal] is egested through the anus

Digestive enzymes

Amylase

• Produced in: Mouth / salivary glands, Pancreas, Small intestine

• Function: Catalyses the breakdown of starch into sugars

---

Trypsin (Protease)

• Produced in: Pancreas, Small intestine

• Function: Catalyses the breakdown of proteins into amino acids

---

Pepsin (Protease)

• Produced in: Stomach

• Function: Catalyses the breakdown of proteins into amino acids

---

Lipase

• Produced in: Pancreas, Small intestine

• Function: Catalyses the breakdown of lipids into fatty acids and glycerol

The respiratory system

The respiratory (breathing) system takes air into and out of the body so that

oxygen from the air can diffuse into the bloodstream and carbon dioxide can

diffuse out of the bloodstream into the air.

What happens during inhalation?

• Intercostal muscles contract, pulling the ribcage upwards.

• Diaphragm muscles contract, causing the diaphragm to flatten.

• These two movements cause an increase in the volume of the thorax.

• The pressure decreases below that of the surrounding air, so air enters the lungs.

• Lungs inflate.

What happens during exhalation?

• Intercostal muscles relax, allowing the ribcage to move downwards.

• Diaphragm muscles relax, allowing it to return to its domed shape.

• These two movements cause a reduction in the volume of the thorax.

• The pressure increases, resulting in air leaving the lungs.

• Lungs deflate.

How is are the alveoli adapted?

Alveoli provide a very large surface area for the diffusion of gases.

•​ Thin walls (only one cell thick walls in each alveolus): gases do not have

to diffuse very far

•​Good ventilation with air – increases the concentration of Oxygen

•​ A good blood supply [by capillaries adjacent to alveoli]: ensures that lots of

oxygen is removed quickly and lots of carbon dioxide is supplied quickly to

the alveoli. This maintains the concentration gradients for these gases.

Aerobic respiration

Chemical reactions that breakdown glucose, using oxygen, to release/ transfer energy inside cells

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (as ATP)

Aerobic respiration takes place continuously in both plants and animals.​

Most of the reactions in aerobic respiration take place inside mitochondria

Ways in which energy released during respiration is used up in the body

to build larger molecules from smaller ones

• in animals, to enable muscles to contract

• in mammals and birds, to maintain a steady body temperature in colder

surroundings

• in plants, to build up sugars, nitrates and other nutrients into amino acids, which

are then built up into proteins.

during exercise, changes occur in the body 

the heart rate increases, increasing blood flow to the muscles

the rate and depth of breathing increase 

glycogen stored in the muscles is converted back to glucose 

these changes increase the supply of glucose and oxygen to, and increase the rate of removal of carbon dioxide from, the muscles

​Muscles need more energy.

•​Breathing rate increases to supply more oxygen to muscles for aerobic respiration.

•​More carbon dioxide produced, which reduces pH of blood [carbonic acid in plasma]

•​Increased breathing rate also removes this excess CO2 faster [to keep blood pH constant].

•​During exercise muscles need to respire quickly to release sufficient energy. At first, they respire aerobically as this releases the large amount of energy required.

•​Eventually a limit is reached, as the heart and lungs cannot supply oxygen to the muscles any faster. This creates an oxygen debt in the muscles. This needs to be repaid to oxidize the lactic acid to carbon dioxide and water.  As a result of this oxygen debt, muscles switch to anaerobic respiration.

•​Anaerobic respiration releases a much smaller amount of energy. It also produces lactic acid, which is toxic and causes cramps.Blood flowing through the muscles eventually removes the lactic acid. 

After exercise

•​Continuation of a faster heart rate: required to transport lactic acid in blood from

muscles to the liver

•​Continuation of a faster and deeper breathing rate: this supplies oxygen for aerobic

respiration of lactic acid in the liver

•​Lactic acid is broken down by oxygen to produce carbon dioxide and water.

Anaerobic excersice in plant cells and in some microorganisms 

results in the production of ethanol and carbon dioxide