Energy, Control and Continuity

Glycolysis This is literally the splitting of glucose molecules into pyruvate that contains 3 carbon atoms. Each molecule of glucose is split to produce 2 molecules of pyruvate with a net gain of 2 ATP molecules.

The Link Reaction Pyruvate is oxidised to form acetyl coenzyme A.

The Krebs cycle Electrons and carbon dioxide molecules are removed from acetyl coenzyme A.

The electron transfer chain Transport of electrons down a series of electron carriers transferring energy that is used to produce ATP.

Matrix – The matrix contains the enzymes involved in the oxidation decarboxylation of pyruvate, and in the Krebs cycle.

Enzyme molecules bound to the inner membrane; these carry out electron transport.

Inner Membrane

Cristae – The inner phospholipids membrane is highly folded to form this.

Outer Membrane – The outer membrane controls the passage of materials in and out of the mitochondrion.

Ribosomes

Intermembrane spaces

D.N.A – The D.N.A threads contain the information required for the mitochondria to replicate.

Central nervous system – The brain and the spinal cord.

Stimulus – A change inside or outside an organism that brings about a response in that organism. Examples include; light, sound, chemicals and pressure.

Receptor – A structure that detects a stimulus and initiates a nerve impulse. Examples of receptors include; rod cells in the retina, chemoreceptors on the tongue and in the nose, pressure receptors in the skin.

Effector – A structure which responds to the arrival of a nerve impulse. Effectors are usually muscles or glands.

Sensory Neurone – A nerve cell that carries impulses from a receptor to the central nervous system.

Motor Neurone – A nerve cell that carries impulses from the central nervous system to an effector.

Reflex Action – A rapid, automatic response to stimulus, for example withdrawing your hand after touching something hot.

During Glycolysis, glucose (6C) is oxidised into two molecules of pyruvate (3C) with a net gain of two moles of ATP and reduced NAD.

The pyruvate undergoes oxidative decarboxylation and combines with coenzyme A to produce acetyl coenzyme A (2C).

In Krebs cycle, acetyl coenzyme A (2C) is combined with a 4-carbon acceptor molecule to form a 6-carbon organic acid. This6-carbon acid then undergoes carboxylation and oxidation to regenerate the acceptor molecule.

Reduced NAD is produced during Glycolysis, the formation of acetyl coenzyme A and the Krebs cycle. Reduced FAD is also produced during the Krebs cycle.

Electrons from reduced NAD and reduced FAD are transferred to electron carrier chains on the cristae of the mitochondria. As the electrons pass along these chains of carriers, ATP is generated.

At the end of the electron carrier chain, electrons, protons and oxygen combine to form water.

A total of 36 moles of ATP is produced during respiration of one mole of glucose.

The reactions of photosynthesis can be separated into the light-dependant reactions and the light-independent reactions. Both occur inside the chloroplast.

The internal phospholipid membranes that make up the thylakoids within chloroplasts contain light-absorbing pigments. To maximise light absorption, thylakoids are arranged in stacks called grana.

The light-dependent reactions occur in the grana.

When chlorophyll a molecules absorb light energy, some of their electrons become excited, gaining energy that can be used to carry out chemical reactions.

Energy from excited electrons in chlorophyll a molecules is used tosplit water, producing protons, electrons and oxygen. This reaction, known as photolysis, produces most of the oxygen present in the atmosphere.

Energy from excited electrons in chlorophyll a molecules is also used to produce ATP. This method of producing ATP id known as photophosphorylation.

This same source of energy is used to add to NADP (nicotinamide adenine dinucleotide phosphate) the protons and electrons that have been obtained by splitting water. Reduced NADP is produced; this is a reducing agent that is later used to reduce carbon dioxide to carbohydrate in the light-independent reactions of photosynthesis.

Stroma – the site of the light-independent reactions. The stroma is a fluid containing enzymes that use ATP generated in the light-independent reactions of photosynthesis to fix carbon dioxide into sugar.

Thylakoids – the light-dependent reactions happen here. The thylakoid membrane is a phospholipid bilayer that has many chlorophyll molecules embedded in it. These absorb light energy and then transfer it to other protein molecules. This stage of photosynthesis generates ATP.

Outer Membrane – The outer membrane is a phospholipid bilayer that controls the movement of molecules in and out of the chloroplast.

Starch Grain – Excess carbohydrate made during photosynthesis is temporarily stored as starch grains.

Granum – The thylakoids are arranged in stacks, each called a granum. This greatly increases the efficiency of the light-dependent reactions by capturing most of the light energy hat enters the cell.

The pancreas both monitors and controls blood glucose concentration; the brain is not involved.

Alpha cells in the pancreas detect a fall in blood glucose concentration and respond by secreting the hormone glucagon.

Glucagon activates enzymes in the liver that convert glycogen to glucose.

Beta cells in the pancreas detect a rise in blood glucose concentration and respond by secreting the hormone insulin.

Insulin increases the rate of uptake of glucose by body cells by stimulating the movement of carrier protein from the cytoplasm to the cell surface membrane. These carrier protein molecules move glucose into the cells by facilitated diffusion.

Insulin also activates enzymes in the liver that catalyse condensation reactions that convert glucose to glycogen.

The actions of both insulin and glucagon result in negative feedback, bringing blood glucose concentration back to normal.

When control of blood glucose fails, diabetes can develop. Type 1 diabetes occurs when cells in the Islets of Langerhans are damaged and no longer produce insulin. Type 2 diabetes is a result of cells in the body becoming resistant to the effects of insulin.

Vasoconstriction – nerve impulses in the sympathetic nerves in the hypothalamus cause the smooth muscle in the skin arterioles to contract. Shunt vessels dilate and divert blood away form the capillaries. Blood flow to the surface capillaries is restricted, so less heat lost by radiation from the skin.

Decreased rate of sweating – vasoconstriction reduces blood flow to the sweat glands, so less sweat is produced. Less heat energy form the body will be lost to convert the water in sweat to water vapour.

Piloerection – hairs on the skins surface stand on end. The erector pili muscles in the skin contract, pulling the hairs upright. IN humans this has no effect in conserving heat but in animals this makes the fur thicker so traps a larger layer of air, which acts as an insulator as it is a poor conductor of heat.

There are also behavioural responses such as putting on more layers of clothes. Animals such as sheep, huddle together to keep warm.

Shivering – skeletal muscles contract and relax rapidly, as the muscles are active the rate of respiration increases and extra heat is generated.

Increased metabolic rate – the hormone adrenaline is released causing a rapid increase in the metabolic rate, so more heat is produced.

Vasodilation – nerve impulses in the parasympathetic nerves from the hypothalamus cause smooth muscle in the skin arterioles to relax. Shunt vessels constrict. This increases blood flow to the surface capillaries leading to dilation of the capillaries so more heat is lost from the skin via radiation.

Increased rate of sweating – vasodilation increases the blood flow to the sweat glands. More sweat is secreted onto the surface of the skin where the water in sweat evaporates using the latent heat form the body.

Panting – some animals, particularly dogs and birds, have very few or no sweat glands. They lose heat by panting. Panting consists of very quick, shallow breaths of air, which evaporate water from the tongue and mouth, producing a cooling effect.

Pilorelaxation – hairs on the body’s surface lie fat. Parasympathetic nerves cause the erector pili muscles to relax so the hairs lie close to the body surface. Less air is trapped next to the skin, reducing insulation.

Behavioural responses also occur. Increasing surface area by stretching out is involuntary but most responses are voluntary. Nerve impulses form the peripheral and central thermoreceptors travel to the cerebral cortex in the brain so you become aware you are hot. You may then remove an item of clothing or go for a swim. Other mammals seek shade or roll in mud.

Inactivity – is a behavioural change that results in less muscle contraction so respiration rate in muscles decreases and less heat is produced.

Decreased Metabolic Rate – long-term exposure to high temperature causes the body to release less thyroxine, reducing the metabolic rate.