B4 - Bioenergetics

Photosynthesis definition - the process of creating chemical energy from sunlight.

Photosynthesis general facts:

• Photosynthesis is an endothermic reaction, meaning it takes in energy from its surroundings
• Photosynthesis happens in the leaves of a plant, where the surface area is maximised to make photosynthesis more effective
• Photosynthesis occurs in the chloroplasts in the cell, where the pigment chlorophyll absorbs the light energy needed.

Photosynthesis:

Word equation: Carbon dioxide + Water ------ Glucose + Oxygen

Unbalanced symbol equation: CO2 + H2O ------ C6H12O6 + O2

Balanced symbol equation: 6CO2 +6H20 ------- C6H12O6 + 6O2

(Where the '-----' are, you should have arrows to show the chemical process. You should also have 'sunlight' over the arrow and 'chlorophyll' underneath it, to make sure it's accurate.)

The uses of the glucose produced in this reaction are as follows, and we'll be covering each one in more detail: Respiration, seeds, fruit, storage, cellulose and protein synthesis. (However, respiration will be covered a little later on).

One of the uses of the glucose produced from photosynthesis is for seeds. Glucose is turned into lipids for storing in seeds, where starch is also stored.

Seeds are small embryonic plants enclosed in a 'seed coat', usually with some stored foods, such as starch or other lipds.

When glucose and fructose are combined, you create sucrose, which is stored in fruits. Fruits deliberatly taste nice so animals will consume them and then spread the seeds.

Photosynthesis occurs when there's enough sunlight; therefore, in winter, the rate of photosynthesis is limited and it needs another form of energy. Glucose can be converted into insoluable starch, which can be stored in the roots, leaves and stems of a plant for when photosynthesis isn't happening.

Glucose can be converted into cellulose, which makes up cell walls. Cellulose provides the cell with structual support and protection, as well as acting as a pressure vessel, preventing over-expansion in the cell during osmosis.

When glucose is combined with nitrates from the soil, amino-acids are made. These amino-acids are then turned into protein.

What is a limiting factor?

A limiting factor is something that can impact the rate of photosynthesis (make it slower or faster). 

Limiting factors of photosynthesis:

• Light intensity (how much sunlight the plant gets)
• Carbon dioxide concentration
• Water concentration
• Temperature

Each one of these limting factors has it's own graph to show how it effects the rate of photosynthesis, which will be on the next card...

As you can see here, light intensity and carbon dioxide concentration go up and then go in a straight line. When it's going up, it means that the factor was the thing limiting the rate of photosynthesis. However, when it levels off, it shows us that it's no longer the limiting factor, and that something else is. The graphs of light intensity and CO2 concentration would be the same as water, despite it not being shown on the image. However, temperature is different to the other factors. This is because of the enzymes (chemical catalysts) in the chloroplasts. When enzymes get to hot, they denature, meaning they change shape and can't fufill their job. When the enzymes denature at high temperatures, they decrease the rate of photosynthesis. This is shown by how the graph goes up as the temperature increases the rate of photosyntheis, and then goes down agin when the enzymes denature.

This practical is an experiment that you will have to do as part of your Biology course:

You put pondweed (elodea or cambomba) in a beaker containing sodium hydrogencarbonate 10cm away from an LED lamp, slitting the end of the pondweed and placing it so that it faces the top of the beaker. This lamp is used as it doesn't generate as much extra heat as an ordinary lamp. Make sure that the beaker is 10cm away - this is vital to the experiment.

Give the pondweed around 5 minutes to adjust before switching on the lamp. Measure the number of bubbles per minute for a minute at 10cm away from the lamp. You'll need to do this 3 times to get your average.

Repeat this process at 20cm, 30cm, 40cm and 50cm to see how light intensity affects the rate of photosynthesis. Make sure you repeat it 3 times at each distance - this makes the experiment results more reliable.

You can then plot the mean number of bubbles per minute at each distance on a graph to show your results. You should notice that at each distance, the number of bubbles per minute falls by a factor of 4 each time (4 times the amount). This is the inverse - square law.

What is respiration?

(Cellular) respiration is the process of producing energy in an organism (plant, animal or human)

• Respiration is an exothermic reaction, meaning it releases energy into its surroundings. 
• Respiration takes place continually in all living cells (it doesn't stop at night, unlike photosynthesis).
• There are two types of respiration that you will need to know, which we will cover in the next few cards.

Aerobic respiration is respiration that uses oxygen, and this is the type of respiration that we experience every day. The equations to show aerobic respiration is as follows:

Word eqution: Glucose + oxygen ---- Carbon dioxide + water

Unbalanced symbol equation: C6H12O6 + O2 ---- CO2 + H20

Balanced symbol equation: C6H12O6 + 6O2 ----- 6CO2 + 6H20 

You might have noticed something familiar about the equation above...it's the exact opposite of the photosynthesis equation (which is handy for us!).

Aerobic respiration releases lots of energy because the glucose molecules have been fully oxidised.

 When you haven't got enough oxygen for aerobic respiration, you start to use anaerobic respiration. This is respiration without oxygen. 

There are two types of anaerobic respiration: anaerobic respiration is muscles and anaerobic respiration in plant & yeast cells.

Anaerobic respiration in muscle cells:

Word equation: Glucose ---- Lactic Acid (+ energy)

Symbol equation: C6H12O6 ---- 2C3H6O3

Anaerobic Respiration in plant & yeast cells:

Word equation: Glucose ---- Ethanol + Carbon Dioxide (+ energy)

Symbol equation: C6H12O6 ----- 2C2H50H + 2CO2

Anaerobic respiration releases less energy because the oxidation of glucose is incomplete. 

Exercise notes:

• When you exercise, your body needs energy so the muscles can contract effectively
• When your body needs more energy, the rate of aerobic respiration increases. To provide extra oxygen, your breathing rate, heart rate and breathing volume increases.

Oxygen Debt:

• However, when anaerobic respiration starts taking place, the lactic acid stops the muscles from contracting effectively, due to fatigue.
• When your body removes this lactic acid from the muscles, an oxygen debt is created.
• The lactic acid is transported out of the muscles via the bloodstream, and taken to the liver where it's converted back into glucose by as series of chemical reactions.
• Reacting with lactic acid and removing it from the cells requires oxygen.

Definition of oxygen debt: the amount of extra oxygen the body needs after exercise to deal with the accumulated lactic acid.

Metabolism definition: the sum of all the chemical reactions in a cell/body.

The 5 reactions:

• Conversion of glucose to starch, glycogen and cellulose
• Respiration
• Formation of lipids
• Formation of amino-acids and proteins
• Breakdown of excess proteins to form urea for excretion

We'll look at each of these in greater detail...

Glucose is an example of a monosaccharide. Organisms combine these together to make various other polysaccharides:

• Cellulose - used in the cell wall of plant cells
• Glycogen - a form of energy store in the muscles
• Starch - an insoluable store of glucose in plants 

Definiton of lipids: fats and oils; large molecules made from slightly smaller units of fatty acids and glycerol.

Lipids are components of cell membranes,as well as being energy stores, chemical messengers and protection -  they are water-proofing, insulating and act as buoyancy aids.

Definition of amino acids: they are the building blocks of protein.

Amino-acids play a crucial role in almost all biological processes, carrying out functions such as giving cells their structure, playing a role in enzymes, building and repairing tissues as well as making antibodies and hormones

Definition of urea: Urea's produced in the liver, when excess proteins are broken down.

Kidneys remove urea from the blood and make urine, which is temporarily stored in the bladder. Urea is important in correcting kidney function, which allows ions and water to be reabsorbed.