Lesson 9: Energy and Photosynthesis
1.Video Lesson
2.Objective
At the end of this lesson , you will be able to:-
Define cellular metabolism and photosynthesis.
Explain anabolic and catabolic pathways in cellular metabolism.
Describe the external and internal structure of a leaf.
Describe the different chlorophyll pigments involved in the absorption of light energy.
Analyse an absorption spectrum of the chlorophyll pigments from the graph.
Brainstorming question
- How do metabolic pathways interact with photosynthesis in plants, and what are the implications of these interactions for overall plant growth and energy storage?
- How do variations in environmental factors (such as light, temperature, and CO₂ levels) affect the metabolic rates of photosynthetic organisms, and what adaptations might be necessary for survival in changing climates?
key words
- Metabolism: The sum of all chemical reactions that occur within each cell of an organism, enabling the cell to produce energy for vital processes and synthesize new organic materials.
- Catabolic Reaction (Catabolism) is the set of reactions involved in the breakdown (destructive phase) of complex molecules into simpler substances, releasing energy in the process.
- Anabolic Reaction (Anabolism):The set of reactions involved in the synthesis (constructive phase) of complex molecules from simpler ones, requiring energy.
- Chlorophylls: Main pigments capturing sunlight.
- Carotenoids: Accessory pigments assisting chlorophyll.
- Phycobilins: Water-soluble pigments in cyanobacteria and red algae.
- Chlorophyll a: Found in all plants, algae, and cyanobacteria.
- Chlorophyll b: Found in green algae and plants.
- Chlorophyll c: Found in photosynthetic members of Chromista and dinoflagellates.
Metabolism
Metabolism is the sum of chemical reactions that takes place within each cell of an organism. The chemical reactions enable cells to produce energy for vital processes and also synthesize new organic materials.
Broadly, these reactions can be divided into two groups
- Catabolic reaction
- Anaolic reaction.
Anabolism is the set of reactions involved in the synthesis (constructive) of complex molecules, starting from the small molecules inside the cells of an organism. Anabolic reactions help in the building of macromolecules like proteins, nucleic acids, and polysaccharides
Catabolism is the set of reactions involved in the breakdown (descrctive) of complex molecules like proteins, gacids, glucose, and fatty acids, respectively. It is also the breakdown of monomers into carbon
| | Anabolism It is the constructive phase of metabolism. | catabolism It is the metabolism. destructive | ||||
| | It is the process whereby simpler substances are joined together to form complex macromolecules. | It is the process whereby complex macromolecules are broken down to form simpler substances or monomers. | ||||
| | The process requires energy to construct substances. | The process releases energy as a result of the breakdown of molecules. | ||||
| | It is an endergonic absorbing) reaction. | It is an exergonic (energy-releasing) reaction. | ||||
| | It occurs during photosynthesis. | It occurs during cellular respiration. | ||||
Photosynthesis
Photoynthesis is a sense of chemical reactions that use light energy to assemble CO2 into glucose (C6Hl206) and other carbohydrates. The plant uses water in the process and releases oxygen gas (O2) as a byproduct. The reaction seems like below
This provide food for plant but also the energy, raw materials, and O2 that are used to support most heterotrophs. Plants, multicellular algae, some protists, Cyanobacteria, and Purple sulfur bacteria are Photoautotrophs. Most of photosynthesis takes place in the leaf.
External and Internal Structure of the Leaf
External structure of leave has the following parts (figure 19)
- epidermis
- Leaf base
- leaf lamina
- petiole
The outer leaf layer is known as the epidermis. This epidermis secretes a waxy waxy cuticle to provides protection & waterproof to protect the organ from drying out. There is a small pore that used for exchanging of water vapour & gases is called stomata. The opening and closing of stomata controlled by Guard cell.
Internal structure of leaf
The internal structure of leaf consists of the following parts that shows in figure 20
- palisade mesophyll
- Spongy mesophyll
The mesophyll is made up of specialised parenchyma cells found between the lower and upper epidermis of the leaf. They are of two types, Spongy mesophyll and spongy mesophyll.
Palisade mesophyll cells are near the upper surface of the leaf where they receive more sunlight. Most of photosynthesis takesplace palisade layers because it contains more chloroplasts than spongy mesophyll cells.Spongy mesophyll is so-called because in three dimensions it is spongy in appearance, because it has many large air spaces between the cells and most gases exchange takes place
The site of photosynthesis
In plants, the highest density of chloroplasts is found in the mesophyll cells of leaves. chloroplast is a double membrane organelle. Chloroplasts have two main parts
- Stroma.
- Cristae
The stroma is a fluid-filled matrix where the light-independent stage of photosynthesis takes place. Within the stroma are a number of other structures such as grains. Within the stroma, another set of membranes form disk-shaped compartments known as thylakoids (Figure 3.4). The interior of a thylakoid is called the thylakoid lumen. In most plant species, the thylakoids are interconnected to form stacks called grana. The grana are stacks of up to 100 disc-like structures called thylakoids where the light-dependent stage of photosynthesis takes place. Within the thylakoids is the photosynthetic pigment called chlorophyll. Some thylakoids have tubular extensions that join up with thylakoids in adjacent grana. These are called inner granal lamellae.
Photosynthetic pigments
Photosynthetic cells contain special pigments that absorb light energy. Different pigments respond to different wavelengths of visible light. Pigments are chemical compounds which reflect only certain wavelengths of visible light. This makes them appear “colorful”. Flowers, corals, and even animal skin contain pigments which give them their particular colors. Pigment have its own importance rather than reflection, to absorb certain wavelengths.In plants, algae, and cyanobacteria, pigments are the means by which the energy of sunlight is captured for photosynthesis. Each pigment reacts with only a narrow range of the spectrum, there is usually a need to produce several kinds of pigments, each of different color,to capture more solar energy. There are three basic classes of pigments. These are:-
- Chlorophylls
- Carotenoid
- phycobilin
.
Chlorophylls are greenish pigments which contain a porphyrin ring. This ring has the potential to gain or lose electrons easily and whereby providing energized electrons to other molecules. There are several kinds of chlorophyll,(a,b and c) which the most important one is chlorophyll “a”. Found in all plants, algae, and cyanobacteria. Chlorophyll “b” occurs only in “green algae” and in plants. The third form of chlorophyll called chlorophyll”c”, is found only in the photosynthetic members of the Chromista and dinoflagellates.
Carotenoids are usually red, orange, or yellow pigments and which gives colors of carrots. Carotenoids cannot transfer sunlight energy directly to the photosynthetic pathway, but must pass their absorbed energy to chlorophyll. Due to this called accessory pigments. e.g. fucoxanthin, the brown pigment whose colors keep other brown algae as well as the diatoms.
Phycobilins arewater-soluble pigments, and are, therefore, found in the cytoplasm, or in the stroma of the chloroplast. They occur only Cyanobacteria & Rhodophyta
