Download Photosynthesis

Photosyntesis
Photosynthesis captures energy for life on Earth. Many chemicals are made to
allow life processes to occur in plants. These chemicals can move in and out of
cells by the process of diffusion. Osmosis is a specific type of diffusion.
Photosynthesis
Photosynthesis is a process used by plants in which energy from sunlight is used to convert
carbon dioxide and water into molecules needed for growth. These molecules include
sugars, enzymes and chlorophyll.
(Enzymes are biological molecules (proteins) that act as catalysts and help complex reactions
occur everywhere in life. Let's say you ate a piece of meat. Proteases would go to work and
help break down the peptide bonds between the amino acids).
Light energy is absorbed by the green chemical chlorophyll. This energy allows the
production of glucose by the reaction between carbon dioxide and water. Oxygen is also
produced as a waste product.
This reaction can be summarised in the word equation:
Carbon dioxide + water
glucose + oxygen
Photosynthesis - Higher tier
The chemical equation for photosynthesis is:
6CO2 + 6H2O
C6H12O6 + 6O2
Glucose from photosynthesis
Glucose is made up of carbon, hydrogen and oxygen atoms. Glucose made by the process of
photosynthesis may be used in three ways:
1. It can be converted into chemicals required for growth of plant cells such as
cellulose
2. It can be converted into starch, a storage molecule, that can be converted back to
glucose when the plant requires it
3. It can be broken down during the process of respiration, releasing energy stored in
the glucose molecules
Autotrophs and Heterotrophs
Organisms are divided into autotrophs and heterotrophs according to their energy pathways.
Autotrophs are those organisms that are able to make energy-containing organic molecules from
inorganic raw material by using basic energy sources such as sunlight. Plants are the prime
example of autotrophs, using photosynthesis. All other organisms must make use of food that
comes from other organisms in the form of fats, carbohydrates and proteins. These organisms
which feed on others are called heterotrophs.
Endergonic
Chemical reactions are occurring all around you and inside you - even at this very moment as
you read this lesson. For example, your stomach is using acid to break down the molecules of
food for digestion. Another common chemical reaction that occurs in nature is photosynthesis, or
when plants convert sunlight into usable energy. All chemical reactions involve energy. An
endergonic reaction is a reaction that requires energy to be absorbed in order for it to take place.
Endergonic reactions are not spontaneous. This means they require work or an input of force often in the form of energy - for them to get started. Sometimes the initial energy required to get
the reaction started is all of the energy that is required, while other times the reaction continues
to absorb energy throughout the entire process.
Examples of Endergonic Reactions
Photosynthesis
One of the most common examples given in biology of an endergonic reaction is the process of
photosynthesis. Photosynthesis is used by all plants to convert light energy into a form of chemical energy
that can be used to fuel their life processes.
Photosynthesis does not happen spontaneously. For example, if you take a plant and cover it with a black
garbage bag and put it in a dark room, the plant will eventually die. Why do you think this happens? The plant
cannot spontaneously make food or complete its life processes without an input of light energy to fuel the
process. Once a plant emerges from the soil and begins to grow, it depends on light.
It is important to note that plants have all of the materials and organelles for photosynthesis to occur inside of
them at all times. However, they simply cannot complete the process without the input of light energy. This
makes photosynthesis an endergonic reaction.
Exergonic
a process wherein the system absorbs energy from the surroundings.
Exergonic Reactions
Do you know what gasoline, sugar, and lipids have in common? Each of these chemicals provides energy for
various systems. Whether it is powering a car for driving or powering animal systems for living, these
chemicals, and many others, store energy in their bonds that can be used once released. In order to release this
energy, these chemicals must undergo exergonic reactions.
Definition
Exergonic reactions are chemical reactions that release energy in the form of heat. Typically, this energy is
released when bonds are broken. More specifically, in humans, these reactions are called catabolic, which
means that the molecules are being broken down into smaller components. By breaking these bonds, systems
(such as the human body or the car example above) can receive the energy need to perform its function(s).
Energy stored in bonds is known as free energy, or energy available to do work. It is also often referred to as
Gibbs Free Energy. When a molecule has a large amount of free energy, it becomes unstable, as the energy
would prefer to be released than stored in bonds. As a rule of thumb: the more free energy in the bond, the
more unstable the molecule will be.
Aerobic Respiration
Definition
Picture yourself working out. Are you lifting heavy weights? Stretching your muscles? Or maybe you're
performing an activity that causes you to sweat and breathe hard, that makes your blood pump through your
veins as it carries oxygen to your muscles to keep you going. If you're performing this last activity, then you're
engaging in aerobic exercise.
Aerobic exercise is any physical activity that makes you sweat, causes you to breathe harder and gets your
heart beating faster than at rest. It strengthens your heart and lungs and trains your cardiovascular system to
manage and deliver oxygen more quickly and efficiently throughout your body. Aerobic exercise uses your
large muscle groups, is rhythmic in nature and can be maintained continuously for at least 10 minutes.
Before going into the benefits of aerobic exercise, let's break down some key terms mentioned above:
Cardiovascular system - is made up of your heart and blood vessels e.g., arteries, veins, and capillaries that
transports blood throughout the body.
Aerobic - refers to how your body uses oxygen to sufficiently meet energy demands during exercise.
Aerobic respiration needs oxygen. It is the release of a relatively large amount of energy in
cells by the breakdown of food substances in the presence of oxygen:
glucose + oxygen → carbon dioxide + water
C6H12O6 + 6O2 → 6CO2 + 6H2O
Aerobic respiration happens all the time in animals and plants. Note that respiration is different
to breathing (ventilation). Most of the reactions in aerobic respiration happen
inside mitochondria in cells.
Benefits
In addition to strengthening your heart and cardiovascular system, participation in regular aerobic exercise has
many health benefits. Aerobic exercise:
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Improves your circulation and helps your body use oxygen better
Increases energy
Increases endurance, which means you can workout longer without getting tired
Helps reduce the risk of developing heart disease
Helps reduce the risk of developing diabetes
Helps reduce body fat
Helps you reach and maintain a healthy weight
Helps reduce stress, tension, anxiety and depression
Improves sleep
Examples
Physical activity such as walking, jogging, indoor cycling or aerobic dancing are all examples of aerobic
exercise that strengthen the heart and lungs, therefore improving your body's utilization of oxygen. For general
health, aim for a 30-minute workout (or three 10-minute workouts per day) three to five days a week at
moderate intensity. Moderate intensity refers to an activity that will increase your breathing and get your
heart beating fast. You should be able to talk with ease during moderate intensity workouts, though trying to
sing would be more challenging.
For weight loss, gradually work up to 45 minutes or longer at moderate to vigorous intensity five to six days a
week, allowing for at least one day of rest a week. Vigorous intensity refers to an activity that will have your
heart beating quite a bit more than moderate intensity workouts, and your breathing will be harder so saying
more than a few words will be difficult.
Anaerobic respiration
Unlike aerobic respiration, anaerobic respiration does not need oxygen. It is the release of a
relatively small amount of energy in cells by the breakdown of food substances in the absence of
oxygen.
Anaerobic respiration in muscles
Anaerobic respiration happens in muscles during hard exercise:
glucose → lactic acid
C6H12O6 → 2C3H6O3
Glucose is not completely broken down, so much less energy is released than during aerobic
respiration.
There is a build-up of lactic acid in the muscles during vigorous exercise. The lactic acid needs
to be oxidised to carbon dioxide and water later.
This causes an oxygen debt - known as excess post-exercise oxygen consumption (EPOC) - that
needs to be ‘repaid’ after the exercise stops. This is why we keep on breathing deeply for a
few minutes after we have finished exercising.
Anaerobic respiration in plants and yeast
Anaerobic respiration also happens in plant cells and some microorganisms. Anaerobic
respiration in yeast is used during brewing and bread-making:
glucose → ethanol + carbon dioxide
C6H12O6 → 2C2H5OH + 2C02
Ethanol is the alcohol found in alcoholic drinks like beer and wine. In bread-making, bubbles of
carbon dioxide gas expand the dough and help the bread rise.
Anaerobic respiration by yeast helps bread dough rise
The table summarises some differences between the two types of respiration.
Aerobic
Oxygen
Needed
Glucose
breakdown Complete
Anaerobic
Not needed
Incomplete
End
product(s)
Carbon
dioxide and
water
Animal cells: lactic
acid. Plant cells and
yeast: carbon dioxide
and ethanol
Energy
released
Relatively
large
Relatively small
amount
Aerobic
Anaerobic
amount
Aerobic respiration releases 19 times more energy than anaerobic respiration from the
same amount of glucose.