BIOLOGY A2

Plants use solar energy to combine water & CO2 in PS. 

Plants & animals break down the organic molecules from PS to make ATP- source of energy  

Energy is ‘ability to do work’.

Cannot be created or destroyed Can be changed from one form to another

Can take variety of forms e.g. light, heat, magnetic.

 ORGANISMS NEED ENERGY FOR:

• Metabolism – all reactions require energy
• Maintenance of body temperature (birds, mammals)
• Production of substances e.g hormones, enzymes
• Maintenance, repair, division of cells
• Active transport
• Movement – of whole organism or within organism

Light energy from sun converted into chemical energy by plants during PS.

Organic molecules from PS converted to ATP during respiration

ATP used by cells to perform work.

 ATP     + (H2O) ->    ADP      + Pi    + E  

Adenosine       +  water     ->    adenosine     +  inorganic    + ENERGY

Triphosphate                           Diphosphate     phosphate

The bonds between groups are unstable so have low activation energy, broken easily =HYDROLYSIS reaction. When the bond is broken large amounts of energy released.

Adenosine triphosphate has 3 phosphate groups

 Conversion of ATP ->ADP is reversible

 As water is removed in the process so called CONDENSATION reaction

          •Making ATP from ADP happens in 3 ways:

• Photophosporylation – in chloroplasts during PS (plants only)
• Substrate level phosphorylation – phosphate groups transferred from donor molecules e.g formation of pyruvate in glycolysis (PC)
• Oxidative phosphorylation – in mitochondria during electron transport (both plants & animals)

The first 2 processes use energy released from movement/transfer of e- along a chain of electron carrier molecules in either mitochondria or chloroplasts.

•Immediate energy source – fats, carbohydrates, glycogen better suited for stored energy. They are short lived due to instability of phosphate group. Much better immediate energy source than glucose because…  

1.Each ATP releases less energy so smaller, more manageable quantities.

2.Hydrolysis of ATP à ADP is single reaction so immediate release of energy – glucose breakdown is series of reactions, so longer.  

Cells containing many mitochondria – muscle fibres, small intestine epithelium – ATP made in cells in high quantities – for movement & active transport. 

•Metabolic processes – build up of macromolecules.  e.g. polysacc from monosacc, polypeptide from amino acids, DNA/RNA nucleotides

•Active transport – change of shape of carrier proteins in membranes. Ions moved against conc. gradient.

•Movement – muscle contraction. Energy needed for sliding filaments. 

•Activation of molecules – enzyme-controlled reactions occur more readily due to lower activation energy.

Secretion – formation of lysosomes

(MAMAS)

Within chloroplasts.

 Leaves are adapted to bring raw materials (carbon dioxide, light, water) & remove oxygen and glucose by having adaptations:

Large SA for max sunlight; Branched leaves so no overlapping/shadowing; Thin so short diff pathway; Transparent cuticle to let light through to PS cells (mesophyll); Long narrow palisade cells with numerous chloroplasts to collect sunlight; Numerous stomata for gas exchange; Stomata that open/close to respond to varying light intensities; Many air spaces in lower mesophyll layer for diffusion of O2 & CO2; Network of xylem to bring water to leaf & phloem to carry sugars away

 Main stages:

Capturing of light energy by chloroplast pigments such as chlorophyll

Light independent reaction – hydrogen ions are used to reduce CO2 .

Light dependent reaction – light energy converted to chemical energy. Involves photolysis. Products are reduced NADP, ATP, oxygen

6CO2  + 6H2O à C6H12O6 + 6O2

 Chloroplasts – disc shaped, long, thin, double membrane,  

GRANA – stacks of up to 100 thylakoid discs (light dependent stafe of PS). Chlorophyll within thylakoids. Some join to adjacent thylakoids, via tubes called inter-granal lamellae.    

STROMA – fluid filled matrix (for light independent stage) . Starch grains present.