Chapter 2: Energy and ATP

Question 0

Why do organisms need energy?

Answer 0

• metabolism- all reactions that take place in living organisms involve energy
• movement- within and of the organism itself
• active transport of ions and molecules, over a plasma membrane, against a concentration gradient
• maintaining body temperature in birds and mammals- endothermic and need energy to replace lost heat
• maintenance, repair and division of cells and organelles
• production of substances used within body (enzymes, hormones)

Question 1

What is energy?

Answer 1

Energy is 'the ability to do work'.
• takes a variety of forms
• cannot be created or destroyed
• can be changed from one form to another
• measured in joules

Question 2

How does energy flow through living systems?

Answer 2

1. ) light energy from the sun is converted into chemical energy in plants, during photosynthesis
2. ) chemical energy, from photosynthesis, in the form of organic molecules is converted into ATP during respiration in cells
3. ) ATP used for useful work in cells

Question 3

What is ATP and how is it stored?

Answer 3

• adenine triphosphate
• made up of one adenine group and 3 phosphates
• bonds between the phosphate groups are unstable and have low activation energy: easily broken.
• water is used to break the bonds (hydrolysis) and convert ATP into ADP
• when these bonds are broken a considerable amount of energy is released

Question 4

How is ATP synthesised?

Answer 4

• the conversion of ATP to ADP is reversible
• energy can be added to make ATP
• water is removed (condensation)

Question 5

What are the three ways in which a phosphate is given to ADP for ATP synthesis?

Answer 5

• photophosphorylation: occurs during photosynthesis, in the cells that contain chlorophyll
• oxidative phosphorylation: occurs in the mitochondria of plant/animal cells during electron transport
• substrate level phosphorylation: occurs in plant/animal cells when phosphate groups are given to ADP to make ATP, from donor molecules

Question 6

Is ATP a long term energy source or an immediate energy source?

Answer 6

Although the instability of the phosphate bonds make ATP a good energy donor, they are also the reason why it is not a good long term energy source (fats and carbohydrates like glycogen are better for this).
It is classed as the immediate energy source and so the cells do not store large quantities of it, but just a few seconds supply. This is because ATP is rapidly re formed from ADP and a phosphate.

Question 7

Why is ATP a better immediate energy source than glucose?

Answer 7

• ATP releases less energy than glucose, in smaller and more manageable quantities.
• the hydrolysis of ATP into ADP is a single reaction and immediate energy is released. The breakdown of glucose occurs in a series of reactions and energy release takes longer.

Question 8

ATP is a source of energy for:

Answer 8

• metabolic processes: provides the energy needed to build macromolecules from their basic units. (Polysaccharides from monosaccharides, polypeptides from amino acids, DNA/RNA from nucleotides).
• movement: provides the energy for muscle contraction. ATP is used to provide the energy for the muscle filaments to slide past one another, this shortening to length of the muscle fibre.
• active transport: provides energy to change the shape of carrier proteins in plasma membrane which allows molecules and ions to be moved against a concentration gradient.
Secretion: needed to form the lysosomes for the secretion of cell products.
Activation of molecules: when a phosphate is transferred from ATP to another molecule, it makes the other molecule more reactive and lowers it’s activation energy, thus allowing enzyme catalysed reactions to occur more readily.