GENERAL BIOLOGY 1
Discovering Photosynthesis (The process behind plants producing their own food and oxygen.)
Photosynthesis is the process used by plants to create their own food. Plants use sunlight, water, and
carbon dioxide to create food (glucose) and oxygen. Photosynthesis takes place in the cells of leaves within the
CHLOROPLAST.
ANATOMY OF A LEAF
TRIVIA: Stomata allow for gas exchange to occur, mainly carbon dioxide to enter the plant to make food
molecules such as glucose and for oxygen to be released by the plant. Plants need to open and close the
stomata. Xylem carries water and minerals from the roots to the leaves. Whereas, phloem carries the food
prepared by the leaves to different parts of the plant.
Metabolism refers to a series of chemical reactions that occur in a living organism to sustain life. The metabolic
processes help in growth and reproduction and help in maintaining the structures of living organisms.
TWO TYPES OF METABOLIC PATHWAYS
1. Catabolic/Catabolism/Exergonic Reaction: Large molecules are broken down into small molecules.
Energy is released. Example: Cellular Respiration
2. Anabolic/Anabolism/Endergonic Reaction: Small molecules are assembled into large molecules. Energy
is required. Example: Photosynthesis
The Photosynthesis Reaction
The photosynthesis reaction converts carbon dioxide and water into glucose and oxygen.
Anatomy of a Chloroplast
2 stages/phases of Photosynthesis
1. Light-dependent reaction - (photochemical phase, photosynthesis reaction or light reaction)
2. Light-independent reaction - (biosynthetic phase, Calvin Cycle or dark reaction)
LIGHT REACTION
During light-dependent reactions, light energy gets converted into chemical energy, and a formation of
ATP and NADPH (Nicotinamide Adenine Dinucleotide Phosphate Hydrogen). Light reaction occurs in the
thylakoids of the chloroplast. The photosystem is the arrangement of pigments including chlorophyll within
thylakoids, simply known as light-absorbing pigments of thylakoids. When a chlorophyll molecule in the thylakoid
membrane is excited by light, the energy level of an electron in its structure is boosted. The packet of excitation
energy now migrated rapidly through the light harvesting pigment molecules to the reaction center of
photosystem where it causes an electron to acquire the large amount of energy.
Energy in light reaction can be used in these ways:
1. Generate ATP
2. Reduced NADP+ into NADPH
This happens in two ways:
1. Photosystems II - These are protein complexes absorbing light energy. They function in the dissociation
of water molecules. Seen at the inner surface of the grana thylakoid membrane. Primary electron
acceptor: Plastoquinone (Pq) and cytochrome complex.
Light energy is trapped in Photosystem II and boosts electron to a higher level. It then splits water by
taking 2e- from it. The electrons are passed from one acceptor to the next to Photosystem I. The electrons
are received by an electron acceptor. Thus, leaving the chlorophyll molecule positive.
2. Photosystems I - These use light energy to convert NADP+ to NADPH2. Also, production of ATP. Seen
at the outer surface of the grana thylakoid membrane. NO PHOTOLYSIS/SPLITTING OF WATER.
Primary electron acceptor: Fd (Ferredoxin) and Plastoquinone (Pq). NADPH will now use in Calvin Cycle.
The light energy in Photosystem I boosts the electrons to an even higher level. The electrons are received
by another acceptor and these combine with the protons from the split water to reduce NADP called non
cyclic photophosphorylation. Any left-over electrons will return to Photosystem I (via electron transport
chain) to produce more ATP. This is called cyclic photophosphorylation.
DARK REACTION
Dark reaction is also called carbon-fixing reaction or Calvin cycle. It occurs in the stroma of the chloroplast
where they utilize the products of the light reaction. In the Calvin cycle, RuBP, is a 5-carbon molecule that is
involved in the Calvin cycle, which is one of the photosynthesis's light-independent processes. With the aid of
an enzyme called RuBisCO, atmospheric carbon dioxide is coupled with RuBP to generate a 6-carbon molecule.
The 6-carbon molecule will be converted into glucose, the final product of the Calvin cycle/dark reaction.
WHAT ARE THE FUNCTIONS OF PHOTOSYNTHESIS?
1.
2.
3.
4.
Photosynthesis converts radiant or solar energy into chemical energy.
Productivity of agricultural crops directly depends upon the rate of photosynthesis.
It provides oxygen in atmosphere for all living organisms.
It maintains the balanced level of oxygen and carbon dioxide ecosystem.
CELLULAR RESPIRATION (The biochemical processes of the cell.)
AEROBIC VS. ANAEROBIC RESPIRATION
CELLULAR RESPIRATION
The process of extracting energy in the form of ATP from the glucose in the food you eat.
MITOCHONDRION - The powerhouses of the cell. Act like a digestive system which takes in nutrients, breaks
them down, and creates energy rich molecules for the cell. Many of the reactions involved in cellular respiration
happen in the mitochondria.
THREE STAGES OF CELLULAR RESPIRATION
1. Glycolysis - Glycolysis is the splitting, or breakdown of 6-carbon glucose into two 3-carbon pyruvate
molecules. Occurs in the cytoplasm of the cell, and it activates in the presence or absence of oxygen.
The two 3-carbon pyruvate moves into the mitochondrial matrix where pyruvate oxidation takes place.
Pyruvate oxidation is the process of converting two 3-carbon pyruvates into two-carbon acetyl CoA with
the help of an enzyme called pyruvate dehydrogenase. This two-carbon acetyl CoA will proceed in the
process of Krebs Cycle.
2. Krebs cycle - Also known as TCA Cycle (The Citric Acid Cycle). In the presence of oxygen, the acetyl
CoA enters the mitochondria to proceed into the Krebs cycle. The TCA cycle begins when acetyl-CoA
combines with a four-carbon oxaloacetate in order to form the six-carbon compound called citrate or citric
acid. The transfer of the energy in pyruvate, which is the energy initially in glucose, into two energy
carriers, NADH and FADH2.
3. Electron Transport Chain - The use of NADH and FADH2 to generate ATP. Most of the ATP produced
during cellular respiration is made during this stage.
WHAT ARE THE MAIN FUNCTIONS OF CELLULAR RESPIRATION?
1. To break down sugar in the presence of oxygen to release energy in the form of ATP.
2. This process releases carbon dioxide and water as waste products.