Revision: Plant Anatomy and Plant Physiology Science SSLC (English Medium) Class 10 Tamil Nadu Board of Secondary Education

A group of similar cells, along with intercellular substances which perform a specific function, is called a tissue.

A tissue, in biology, is defined as a group of cells that have a similar structure and perform a specific function. The word tissue originates from French, which means "to weave."

A group of similar cells which perform a specific function.
example: Muscular tissue in animals.

A tissue is a group of cells that are similar in structure and are organized together to perform a specific task.

The tissue is a group of cells of similar structure and function.

Vascular tissue is the complex plant tissue in higher plants that are composed of xylem and phloem and is concerned with conducting water, minerals, and organic food throughout the plant body.

• Cells that perform a particular function always live in a group. This group of cells is called a tissue.
• For example, blood, phloem, muscle, etc. are examples of tissues.

Photosynthesis is the process by which living plant cells, containing chlorophyll, produce food substances (glucose and starch) from carbon dioxide and water by using light energy. Plants release oxygen as a byproduct during photosynthesis.

Releasing electrons and dividing the water molecule (H2O) into its two components (Hydrogen and Oxygen). Photolysis is the term used to describe this reaction, which is characterised by the fracturing of molecules by light (photo = light, lysis = breaking).

In the presence of chlorophyll, photosynthesis is the process by which green plants and certain other organisms convert carbon dioxide and water into glucose (a form of sugar) using light energy, typically from the sun. As a byproduct, this process generates oxygen.

Chloroplasts are indeed miniature ovoid structures that are encased in a double membrane. Nevertheless, the response could offer a more succinct definition: Chloroplasts are the cellular organelles that are responsible for the process of photosynthesis in plant cells. They are the sites where photosynthesis occurs and contain thylakoids.

Thylakoids are indeed very small compartments that are present within chloroplasts. They are the locations where the light-dependent reactions of photosynthesis take place and contain chlorophyll. Nevertheless, the response could be simplified to enhance its clarity.

In the presence of chlorophyll, photosynthesis is the process by which green plants and certain other organisms convert carbon dioxide and water into glucose (a form of sugar) using light energy, typically from the sun. As a byproduct, this process generates oxygen.

Photolysis occurs in the grana of a chloroplast and is defined as the splitting of H₂O molecules into hydrogen ions and oxygen in the presence of light.

Photophosphorylation is the process of converting ADP into energy-rich ATP by adding an inorganic phosphate (Pi), using energy from light (photons).

Most green plants use glucose as soon as it occurs during photosynthesis to make starch. Polymerisation is the process by which several glucose molecules are turned into one starch molecule.

The process by which monomer molecules combine together to form a polymer is called polymerisation.

The process by which monomer molecules combine together to form a polymer is called polymerisation.

The process of conversion of many simpler and smaller molecules into a complex, bigger molecule is termed as polymerisation. For example, conversion of several glucose molecules into a starch molecule. 

The process occurring in the cytoplasm where one glucose molecule is stepwise oxidized to form two molecules each of pyruvic acid, ATP, NADH₂, and water is called glycolysis.

The cyclic series of reactions occurring in the mitochondria, where acetyl-CoA is completely oxidized to produce CO₂, H₂O, NADH₂, and FADH₂, is called the tricarboxylic acid cycle or Krebs cycle.

The process occurring in the mitochondria, where NADH₂ and FADH₂ release electrons to form ATP and water, producing 3 ATP from each NADH₂ and 2 ATP from each FADH₂, is called the electron transfer chain reaction.

The ratio of the volume of CO₂ evolved to the volume of O₂ consumed in respiration is called Respiratory Quotient (RQ) or respiratory ratio.

Respiratory quotient (RQ) is the ratio of the volume of carbon dioxide produced to the volume of oxygen consumed in respiration over a period of time.

\[\mathrm{RQ=\frac{Volume~ofCO_{2}~evolved}{Volume~ofO_{2}~consumed}}\]

The balanced chemical equation is: \[6\mathrm{CO}_{2}+12\mathrm{H}_{2}\mathrm{O}\frac{\text{light energy}}{\text{chlorophyll}}\mathrm{C}_{6}\mathrm{H}_{12}\mathrm{O}_{6}+6\mathrm{H}_{2}\mathrm{O}+6\mathrm{O}_{2}\uparrow\]

The balanced chemical equation is: \[6\mathrm{CO}_{2}+12\mathrm{H}_{2}\mathrm{O}\frac{\text{light energy}}{\text{chlorophyll}}\mathrm{C}_{6}\mathrm{H}_{12}\mathrm{O}_{6}+6\mathrm{H}_{2}\mathrm{O}+6\mathrm{O}_{2}\uparrow\]

• Anatomy = Study of Internal Structure - Plant anatomy is the study of the internal structure of plants, which includes the organisation and structure of tissues.
• Basic Unit = Cell - The basic unit of plants is the cell. Cells are organised into Tissues → Organs (organisational hierarchy).
• Tissue Definition - A tissue is a group of similar cells having a common origin that perform a specific function together.
• Monocots vs. Dicots - Anatomical (internal structural) differences exist between monocots and dicots, so it's important to know them separately.
• Internal Structure Adapts - The internal structures of plants adapt according to their environment (e.g., water availability, climate), and structural similarities exist in both external and internal morphology of organisms.

• Tissue variation in plants depends on their location in the plant body, and the structure and function of each tissue is related to where it is found.
• Plants have three main tissue systems: epidermal tissue system, ground (fundamental) tissue system and vascular (conducting) tissue system.
• These three systems are classified based on their structure and location, and each serves a specific purpose in plant anatomy.

• Plastids are present only in plant cells and are of several types—chloroplasts, leucoplasts, and chromoplasts.
• They are double-membraned organelles with a proteinaceous matrix and contain DNA.
• Chloroplasts (green) contain chlorophyll in thylakoids and perform photosynthesis.
• Leucoplasts are colourless, store starch, and have no pigment.
• Chromoplasts are variously coloured, contain pigments like xanthophyll and carotene, and help in pollination by attracting pollinators.

• Photosynthesis converts sunlight into chemical energy using CO₂ and water, producing glucose and releasing oxygen as a byproduct.
• Green plants are autotrophs (make their own food); all other organisms are heterotrophs. All life depends on sunlight for energy.
• Three essentials for photosynthesis: chlorophyll, light, and CO₂.
• Experiment 1 - Variegated leaf tested for starch showed that photosynthesis occurs only in green parts in the presence of light.
• Experiment 2 - Leaf part enclosed with KOH-soaked cotton (absorbs CO₂) tested negative for starch → proved CO₂ is necessary for photosynthesis.

1. Photosynthesis mainly occurs in mesophyll cells (palisade and spongy) of leaves, using chlorophyll to trap sunlight.
2. Carbon dioxide enters the leaf via stomata by diffusion down a concentration gradient.
3. Water is absorbed by roots, transported via the stem to mesophyll cells of the leaves.
4. Using light energy, chlorophyll helps synthesize glucose (C₆H₁₂O₆) from CO₂ and H₂O, releasing O₂ as a by-product.
5. The balanced chemical equation is: \[6\mathrm{CO}_{2}+12\mathrm{H}_{2}\mathrm{O}\frac{\text{light energy}}{\text{chlorophyll}}\mathrm{C}_{6}\mathrm{H}_{12}\mathrm{O}_{6}+6\mathrm{H}_{2}\mathrm{O}+6\mathrm{O}_{2}\uparrow\]

1. Chlorophyll is the green pigment in plants, found in chloroplasts.
2. It is located in the thylakoid walls inside the chloroplasts.
3. Chloroplasts are mainly present in mesophyll cells of leaves.
4. There are nine types of chlorophyll, but chlorophyll a and chlorophyll b are the most common.
5. Chlorophyll absorbs blue and red light for photosynthesis and reflects green light.

1. Photosynthesis mainly occurs in mesophyll cells (palisade and spongy) of leaves, using chlorophyll to trap sunlight.
2. Carbon dioxide enters the leaf via stomata by diffusion down a concentration gradient.
3. Water is absorbed by roots, transported via the stem to mesophyll cells of the leaves.
4. Using light energy, chlorophyll helps synthesize glucose (C₆H₁₂O₆) from CO₂ and H₂O, releasing O₂ as a by-product.
5. The balanced chemical equation is: \[6\mathrm{CO}_{2}+12\mathrm{H}_{2}\mathrm{O}\frac{\text{light energy}}{\text{chlorophyll}}\mathrm{C}_{6}\mathrm{H}_{12}\mathrm{O}_{6}+6\mathrm{H}_{2}\mathrm{O}+6\mathrm{O}_{2}\uparrow\]

• Light Harvesting Complexes (LHC) - Made up of hundreds of pigment molecules bound to proteins. Found in PS I and PS II. Help absorb different wavelengths of light for efficient photosynthesis.
• Antennae System - In each photosystem, all pigments except one chlorophyll a molecule form the antennae (light-harvesting system). They absorb light and pass energy to the reaction centre.
• Reaction Centre - The single chlorophyll a molecule that directly participates in the photochemical reaction. It is different in PS I and PS II.
• PS I - Reaction centre = P700 (absorbs light at 700 nm).
• PS II - Reaction centre = P680 (absorbs light at 680 nm).
• Steps of Light Reaction - Light absorption → Water splitting → Oxygen release → ATP and NADPH production.

• Blackman’s Law of Limiting Factors states that the rate of photosynthesis is controlled by the factor in the least supply.
• Light affects photosynthesis through intensity, quality, and duration; it shows a linear increase at low intensity and saturation at about 10% of full sunlight.
• Carbon dioxide is the major limiting factor; increasing CO₂ concentration increases photosynthesis up to a limit, after which it may become harmful.
• Temperature controls enzymatic reactions (dark reactions); C₄ plants work better at higher temperatures, while C₃ plants have a lower optimum temperature.
• Water affects photosynthesis indirectly; water stress causes stomatal closure, reducing CO₂ availability and decreasing photosynthesis.
• All factors work together, but usually one limiting factor determines the overall rate of photosynthesis.

• Structure - Double membrane-bound organelle. The outer membrane is smooth; the inner membrane has infoldings called cristae. Inner space is called the matrix.
• Shape & Size - Sausage-shaped or cylindrical. Diameter: 0.2–1.0 µm; Length: 1.0–4.1 µm.
• Function - Site of aerobic respiration; produces energy as ATP. Called the 'Powerhouse of the Cell'.
• Matrix Contents - Contains circular DNA, RNA molecules, and 70S ribosomes for protein synthesis.
• Reproduction - Divides by fission.

• Glycolysis (EMP pathway) breaks one glucose (6C) into two pyruvic acid (3C) molecules in the cytoplasm; common to both aerobic and anaerobic respiration.
• It involves 10 enzyme-controlled reactions in two phases — Preparatory and Pay-off.
• Preparatory Phase — Glucose is phosphorylated using 2 ATP and split into two 3C molecules (PGAL + DHAP; DHAP converts to PGAL).
• Pay-off Phase — PGAL is oxidised, NADH₂ is formed, and ATP is produced via substrate-level phosphorylation.
• Net gain = 2 ATP (4 produced − 2 consumed); PEP → Pyruvic acid is the final energy-yielding step.
• Fate of pyruvate — with O₂: enters the Krebs cycle; without O₂: forms lactic acid (muscles) or ethanol + CO₂ (yeast).
• In plants, glucose comes from sucrose (a photosynthesis product), split by invertase into glucose and fructose before entering glycolysis.

• ETS is located in the inner mitochondrial membrane; it oxidises NADH and FADH₂ to release stored energy.
• Electrons from NADH enter via Complex I; from FADH₂ via Complex II - both pass to Ubiquinone (UQ).
• Electrons move: UQ → Complex III → Cytochrome c → Complex IV → finally to O₂ (final acceptor), forming water.
• Movement of electrons pumps H⁺ ions from the matrix to the intermembrane space, creating an electrochemical proton gradient.
• Protons flow back through F₀ into the matrix via ATP synthase (Complex V); energy is used by F₁ to synthesise ATP - this is oxidative phosphorylation.
• Energy yield - 1 NADH = 3 ATP; 1 FADH₂ = 2 ATP.
• Oxidative phosphorylation uses energy from redox reactions, unlike photophosphorylation, which uses light energy.

• It is a common oxidative pathway where acetyl Co‑A (from pyruvic acid via link reaction) is completely oxidised to CO₂.
• The cycle also supplies intermediates (e.g., α‑ketoglutarate, oxaloacetate) for synthesis of amino acids such as glutamate and aspartate.
• Per pyruvic acid, the cycle produces 3 CO₂, 4 NADH + 4H⁺, 1 FADH₂ and 1 ATP (or GTP) in the mitochondrial matrix.
• For each glucose (2 pyruvates), Krebs cycle output is 6 CO₂, 8 NADH + 8H⁺, 2 FADH₂ and 2 ATP molecules.
• Considering the whole respiratory pathway, glucose breakdown yields CO₂, 8 NADH + H⁺, 2 FADH₂ and 2 ATP at the Krebs‑cycle level.
• Because its intermediates are used both for breakdown (catabolism) and for biosynthesis (anabolism), the respiratory pathway is termed an amphibolic pathway.

• Fermentation is the incomplete oxidation of pyruvic acid under anaerobic conditions, found in bacteria, yeast, and muscle cells.
• Alcoholic fermentation (yeast) - pyruvic acid → ethanol + CO₂; enzymes: pyruvic acid decarboxylase and alcohol dehydrogenase.
• Lactic acid fermentation (bacteria/muscles) - pyruvic acid → lactic acid; enzyme: lactate dehydrogenase; causes muscle stiffness.
• In both types, NADH + H⁺ is reoxidised to NAD⁺, which is reused in glycolysis.
• Both release less than 7% of glucose energy; products (alcohol/lactic acid) are hazardous in nature.
• Yeast dies when alcohol concentration reaches 13%; higher alcohol beverages are made by distillation.
• Aerobic respiration fully oxidises glucose in mitochondria using O₂, releasing far more energy than fermentation.

• The electron transport chain is located on the inner mitochondrial membrane and contains a series of electron and proton carrier complexes (I–V).
• Complex I (NADH dehydrogenase) accepts electrons from NADH via FMN and Fe‑S centres, passes them to ubiquinone (Co‑Q), and pumps 4 H⁺ into the intermembrane space.
• Complex II (succinate dehydrogenase) receives electrons from succinate through FADH₂ and Fe‑S centres, passes them to Co‑Q, but does not pump protons.
• Complex III (cytochrome‑c reductase) transfers electrons from reduced Co‑Q (UQH₂) to cytochrome‑c and pumps 4 H⁺ into the intermembrane space.
• Complex IV (cytochrome‑c oxidase) passes electrons from cytochrome‑c to oxygen, reducing it to water and pumping additional H⁺ across the membrane.
• Complex V (ATP synthase) uses the proton gradient generated by complexes I, III and IV to synthesise ATP from ADP and Pi; this proton‑driven ATP formation is called chemiosmosis.
• Oxidation of each NADH yields about 3 ATP, while every FADH₂ yields about 2 ATP, though exact yields can vary with conditions and substrate.

• Respiratory Quotient (RQ) is the ratio of volume of CO₂ evolved to volume of O₂ consumed during aerobic respiration. Formula: RQ = Volume of CO₂ evolved ÷ Volume of O₂ consumed.
• For carbohydrates - RQ = 1 (equal volumes of CO₂ and O₂); e.g., glucose: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy.
• For fats - RQ is less than 1 (more O₂ needed for oxidation); e.g., Tripalmitin: RQ = 102/145 = 0.7.
• For proteins, RQ is approximately 0.9.
• In living organisms, multiple substrates are respired together (not pure fats or proteins), so RQ is often more than 1; pure fats or proteins are never the sole respiratory substrate.