Plant Biology Notes PDF

Unit 2: Plants Characteristics of plants Plants are living things. Plants are multicellular. Plants are eukaryotic organisms Plants are autotrophic (self–feeding). Plants are sessile. Plants practice asexual and sexual reproduction patterns  Flowering and non – flowering plants flower...

Unit 2: Plants Characteristics of plants Plants are living things. Plants are multicellular. Plants are eukaryotic organisms Plants are autotrophic (self–feeding). Plants are sessile. Plants practice asexual and sexual reproduction patterns  Flowering and non – flowering plants flowering plants are : non – vascular limited height and restricted to moist and shaded areas. seedless and do not have flowers and fruits Example mosses and liverworts.  1. Gymnosperm commonly known as the conifers or ‘naked seed Well-developed root stem and leaves but have no flowers. well vascular Their reproductive organ is cone, The seeds produced in their cone (naked seeds). They have small needle-shaped leaves with a thick waxy cuticle that reduces water loss They are evergreen so they can photosynthesize all year long Angiosperms ❖ The biggest group of land plants on the Earth. ❖ Their reproductive structures are carried out in flowers ❖ vascular with well-developed root, stem and leaves ❖ They have flowers and produce seeds within a fruit ❖ Are subdivided into classes of monocotyledons and di cotyledons Structure and function of plant parts The external structure of a typical angiosperm has two major systems. The shoot system The root system: ↂ The shoot system: found above the ground ↂ it includes the organs such as stem, branches, leaves, buds , flowers and fruits ↂ The root system: grows downward into the ground. ↂ It includes ↂ the primary or tap root, ↂ lateral or branch roots, ↂ root hairs and root cap. ↂ Roots are distinguished from an underground stem in that, it does not bear either leaves or buds  The external structure of a typical leaf consists of the petiole (leaf stalk), Lamina provides large surface area, which enables leaf to collect light. creates short distance for gas exchange through the stomata midrib The midrib is harder and contains the vein (transporting vessels) of the leaf as well as supportive tissues with hard cell wall. margin base and tips External structure of a typical leaf ⁂ Roots are the underground part of the plant body that is usually colorless. ⁂ It is primarily responsible for anchoring the plant to the soil, ⁂ absorption of water and minerals, and ⁂ storage of reserve foods ⁂ Basically two types of roots ⁂ Tap-roots ⁂ Adventitious root system ⁂ A tap-root A main root that is larger and grows faster than the branch roots. ⁂ It consists of one large, primary vertical root.. ⁂ Examples: Carrot, radish, beet ⁂ By penetrating deep into the soil, tap roots provide stability (anchorage) and absorb water located deep in the ground. ⁂ Tap root system is a feature of dicot plants ❖ Adventitious root system develops from any part of the plant usually a stem and sometimes a leaf. ❖ The adventitious roots are found in monocot plants where the taproot is short-lived. ❖ Examples: Grass, sugarcane, oak, and ivy. ❖ Based on the origin of the adventitious root, they are further classified into: ❖ Fibrous Roots ❖ Foiler roots ❖ True Adventitious  Fibrous root is usually formed by thin, moderately branching roots growing from stems. Fibrous root is very efficient for absorbing water and minerals close to soil surface. It creates a thick network of roots that are good at holding soil together and protect soil from erosion. Fibrous roots are features of monocot plants Types of roots The internal structure of a leaf The two internal layers of a leaf, are ; Outer lay er( epidermis) middle (mesophyll) layer. ❖ Epidermis, a single layer of tightly packed cells that covers the upper and lower surface of the leaf. ❖ The upper epidermis is covered by a waxy cuticle, which transmits sunlight for photosynthesis but restricts water loss by evaporation. ❖ The lower epidermis contains bean shaped guard cells that leave open spaces known as stomata. 2. middle (mesophyll) layer. It lies between the upper and lower epidermis. It includes tissues that are directly or indirectly involved in photosynthesis. There are two regions in the mesophyll layer Palisade layer spongy layer Palisade layer The palisade layer is composed of regularly arranged and closely packed columnar (vertically elongated) cells. The cells contain the largest number of chloroplasts per cell. As the layer is immediately beneath the upper epidermis, it is in the best position to capture most of the sunlight and this enables it to carry out most of the photosynthesis. The slight but precise separation of the columnar cells maximizes the diffusion of CO2 and capillary movement of H20. Spongy layer Lies below the palisade cells. Spongy cells are irregularly shaped with fewer chloroplasts. They are very loosely arranged with numerous airspaces. These air spaces, which are very close to the stomata allow the diffusion of O2, water vapour and CO2 sit of photorespiration  The internal structure of a stem 1. Epidermis is the outermost layer of the stem. The outer walls are greatly thickened with cuticles, which minimizes the rate of transpiration. The cells are compactly arranged, which protect the underlying tissues from mechanical injury and prevent the entry of harmful organisms. Internal structure of a typical stem Transverse section of the stem Hypodermis lies below the epidermis. It is mainly composed of collencyma cells that are specially thickened at the corners due to the deposition of thick cellulose. This enables the layer to give mechanical strength to the stem. 2. Cortex : ↂ consists of few layers of thin-walled, large, round, or oval cells, having intercellular space and serving for storage of food. 3. Endodermis ↂ Is the innermost layer of the cortex that separates the cortex from the vascular bundles. ↂ The cells are compactly arranged and usually contain starch grains. ↂ Thus, the endodermis serves as a food reserve and may be termed as a starch sheath 4. Vascular bundles ↂ Are longitudinal strands of conducting tissues or transporting vessels, consisting of xylem and phloem arranged in a ring around the central pith 5. Pith – occupies the central portion of the stem, composed of thin walled cells, which are rounded or polygonal, with or without intercellular space. It stores food and helps in the internal translocation of water  The internal structure of a root ❖ peliferous layer is the outermost layer made up of single-layer cells. ❖ The cuticle is absent. ❖ It consists the single-celled root hairs. ❖ Cortex is a multi-layered large zone made of thin-walled oval or rounded loosely arranged cells with intercellular spaces. ❖ It stores food and water. ❖ Endodermis is the innermost layer of the cortex, made of barrel-shaped closely packed cells. ❖ The layer helps the movement of water and dissolved nutrients from the cortex into the xylem. ❖ Pericycle is a single layer inner to endodermis. ❖ It is the site of origin of lateral roots. ❖ Vascular bundles consist of xylem and phloem with meristematic ❖ Pith is present in young roots while absent in old roots.  Reproduction in plants Reproductive structure and life cycle of flowering plants A flower is the reproductive organ of angiosperms, plants with seeds covered by or contained in a fruit. flower has four floral parts, namely Sepals, Petals, Stamen, and Pisti. Types of flower ❖ A complete flower has the four floral parts. ❖ incomplete flower if it does not have any one of the f loral parts. ❖ A perfect flower has both stamen and pistil. ❖ imperfect flower- a flower does not have either stamen or pistil. ❖ An imperfect flower is incomplete flower, but an incomplete flower may or may not be an imperfect f lower. Sepals ( calyx) – usually green leaf-like structure protecting the lower part of female and male parts Petals (corolla) – mostly brightly coloured and attract pollinating agents like insects Stamen (Androecium) – is the male part, consisting of the filament and anther Pistil ( Gynoecium or carpel) – is the female part, consisting of the ovary with ovules, style and stigma.  Pollination Pollination is the process of transferring pollen grains from the male part (anther) of a flower to the female part (stigma) of another or the same flower. This transfer is essential for the reproduction of flowering plants.  Cont… Types of Pollination 1.Self-Pollination: When pollen from the same flower or a different flower on the same plant fertilizes the ovules. 2.Cross-Pollination: When pollen from one plant is transferred to the stigma of another plant. This is more common in nature and often results in genetically diverse offspring.  Agents of Pollination Wind: Many grasses, trees, and weeds are pollinated by wind. They produce large amounts of lightweight pollen that is carried by the wind. Water: Some aquatic plants are pollinated by water. Pollen grains float on the water's surface and are carried to other plants. Animals: Many flowering plants rely on animals, such as insects, birds, bats, and even some small mammals, to pollinate them. These animals are attracted to the flowers by their bright colors, sweet scents, or nectar. Pollen tube formation Plants Pollen grains---- stigma ---- pollen tubes ----style----form the male gamete ----approaches the ovule  Fertilization In plants, fertilization is a process of sexual reproduction, which occurs after pollination and germination. Fertilization can be defined as the fusion of the male gametes (pollen) with the female gametes (ovum) to form a diploid zygote.  Seed and fruit formation Following fertilization and formation of seed embryo, the ovule matures into seed while the ovary matures into a fruit. Thus seed is a matured ovule while the fruit is a matured ovary  Seed dormancy /Seed germination Seed dormancy is the state of seeds that prevents them from germinating under favourable conditions. A dormant seed is inactive and waiting for the favourable condition to start germination. If there is enough water and nutrients the seed will break dormancy and the seed embryo starts to develop into a seedling  Seeds ▪ Describe the structure of seed and embryo List down the difference between dicot and monocot seed ❖ The seed contains three parts: ❖ the seed embryo ❖ cotyledon/endosperm ❖ seed coat  CONT… ⁂ The seed embryo consists of the radicle (future root), epicotyl, hypocotyl and the plumule (future shoot) ⁂ Cotyledon and endosperm are food storing tissues, essential for the seed embryo (future plant) until it forms leaf and starts manufacturing its own food. Dicot seed Monocot seed Two cotyledons are present in Only one cotyledon present the embryo Cotyledons are fleshy and store Cotyledon is very thin and lacks food materials food materials Endosperm is absent Endosperm is large and well developed Primary root produced from the Primary root formed from rad radicle bears many lateral roots. icle is replaced by adventitious 30 fibrous roots  CONT…. Seed Structure A seed is a fundamental unit of plant reproduction. It consists of three primary components: 1. Seed Coat: It protective outer layer is typically tough and impermeable to water, shielding the embryo from environmental factors like desiccation, mechanical damage, and pathogens.  Cont…. The seed coat, also known as the testa, serves several important functions: Protection: It forms a tough outer layer that protects the embryo and endosperm from physical damage, desiccation, and attack by insects, fungi, and bacteria. Dormancy: In some seeds, the seed coat can create a state of dormancy, delaying germination until conditions are favorable for the seedling's survival.  con…. Dispersal: The seed coat may have structures like hooks, spines, or wings that aid in seed dispersal by attaching to animals or catching the wind. Water Uptake: The seed coat can have a micropyle, a small opening that allows water to enter the seed, triggering germination  CONT… 2. Endosperm: Nutrient-rich tissue surrounds the embryo and provides a food source during germination. It is usually rich in carbohydrates, proteins, and fats. 3. Embryo: The most crucial part of the seed, the embryo is the developing plant. It contains all the essential structures for a new plant to grow  Embryo Structure The embryo is composed of several key parts: A. Cotyledons: These are embryonic leaves that function as storage organs for nutrients. The number of cotyledons varies between plant species: ▪ monocots have one cotyledon, while dicots have two. B. Hypocotyl: This is the stem-like structure that connects the cotyledons to the radicle.  CONT… C. Epicotyl: This is the part of the embryo above the cotyledons that will eventually develop into the shoot system, including the stem, leaves, and flowers. D. Radicle: This is the embryonic root that will anchor the plant in the soil and absorb water and minerals.  Seed dispersal Plants at their seed stage display long-distance mobility and they do so with the help of seed dispersal agents. Seed dispersal is an adaptive mechanism of plants that ensures seed will be separated from the parent plants distributed over a large area to safeguard the germination and survival of the seeds to adult plants, thereby minimizing overcrowding at one place. Seeds can be dispersed by animals, wind or water.  Gemination of seed The resumption of active growth of the embryo after a period of dormancy is known as germination. There are three essential conditions for seed germination. Water (moisture) Oxygen ( Aeration) Temperature (warmth)  1. Water (moisture) ❖ Water is important for the germinating seed because the hydration of the seed coat increases its permeability to O2. ❖ Water is essential for the enzymatic hydrolysis of organic food and acts as an agent of transport in the translocation of soluble substances.  2. Oxygen ( Aeration) Oxygen is necessary for aerobic respiration by which the seeds get energy for the growth of the embryo.  3. Temperature (warmth) ❖ Seeds require optimum temperature for germination.  TYPES OF GERMINATION 1. Epigeal germination the cotyledon is pushed up to become the photosynthetic surface of the seedling by the elongation of a region of the embryo. 2. Hypogeal germination the cotyledon remains under the soil.  Photosynthesis ❖ Photo –light ❖ synthesis—making ❖ Photosynthesis is process of making food by green plants ❖ The process of making food by green plants in the presence light energy and chlorophyll ❖ Photosynthesis is the process by which autotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water  The photosynthetic apparatus The internal structure of the chloroplast, which is termed as photosynthetic apparatus.  Cont.. Granum: consists of stacks of flattened sacks, each of which is called thylakoid. The granum contains the chlorophyll, enzymes and co factors that participate in the light trapping phase of photosynthesis. (the light reaction takes place)  Cont.. Stroma: is a gel-like colourless matrix, which is a site for sugar (carbohydrate) synthesis through carbon fixation. It is from the sugar produced in the stroma that is directly or indirectly converted to all organic compounds (including amino acids, proteins and lipids). Feature Grana Stroma Stacked, disc-shaped Structure Fluid-filled matrix thylakoids Inside chloroplasts, Location Inside chloroplasts surrounding grana Site of Site of light-dependent light-independent Function reactions of reactions (Calvin photosynthesis cycle) Contains chlorophyll Does not contain Pigments and other pigments pigments  Contains enzymes Contains enzymes for Enzymes for electron carbon fixation and transport and ATP carbohydrate synthesis synthesis Maintains a low pH pH due to proton Maintains a neutral pH pumping Contains some DNA Genetic Material Contains chloroplast DNA (chloroplast DNA) Highly folded membrane system No internal membrane Membrane System for increased system surface area  Cont… Stroma Lamellae : Single, unstacked thylakoids that connect different grana. Contain lower concentrations of chlorophyll. Primarily involved in the cyclic electron transport chain. Both grana and stroma lamellae are essential components of the thylakoid membrane system. The interconnected network of lamellae maximizes the surface area for light absorption and energy conversion. The light absorbing system in chloroplast light absorbing pigments, mainly chlorophyll and sunlight absorbed serves as agent of photochemical reaction in food synthesis (photosynthesis). The chloroplast contains chlorophyll (particularly chlorophyll a and b) and other light absorbing accessory pigments capable of absorbing light at different wavelengths. Accessory pigments are light-absorbing compounds found in photosynthetic organisms that work in conjunction with chlorophyll a. They expand the range of light wavelengths that can be absorbed for photosynthesis. Types of Accessory Pigments: A. Chlorophyll b: Similar to chlorophyll a but absorbs different wavelengths of light. Contributes to the overall light-harvesting capacity of the plant. Carotenoids: These pigments absorb blue and green light, reflecting yellow, orange, or red hues. They protect chlorophyll from photooxidation, a process that can damage the pigment. Examples include beta-carotene and xanthophylls. Function of Accessory Pigments: Broadening the Light Absorption Spectrum: By absorbing light at wavelengths that chlorophyll a cannot, accessory pigments increase the overall efficiency of photosynthesis. Photoprotection: They protect chlorophyll from photooxidative damage by dissipating excess light energy as heat. Antioxidant Properties: Some carotenoids act as antioxidants, protecting the plant from oxidative stress  Cont… The light absorbing pigments of chloroplasts absorb most of the visible light, ranging from 400 – 700 nm. Maximum light absorption occurs at wavelengths from 400 – 500 nm and 600 – 700 nm, blue and red light respectively. Light ranging from 500 to 600nm that includes green light is not absorbed, it is rather reflected. Mechanism of photosynthesis Photosynthesis consists of a number of photochemical and enzymatic reaction. It is the sum total of the following two sub reaction  CONT…. 1. Light reaction this is also known as the light dependent stage, ❑ It takes place in the granum, where the light absorbing system – mainly chlorophyll occurs. Here, the granum is organized as Photosystems and Electron Transporting System. ❑ The photosystem consists of chlorophyll that absorbs sunlight maximally at blue and red range of light spectrum.  CONT… Split of water molecules (H2O) into H+ and O2. This is known as photolysis. The O2 is released to the atmosphere through leaf stomata. excite some electrons in the chlorophyll molecule to higher energy level which pass down the ETS and generate high energy ATP molecule. The ATP and H+ harvested during light reaction will be used as an input in the Stroma where conversion of CO2 to carbohydrate takes place.  The chemical equation for the light reaction of photosynthesis is: 2H₂O + 2NADP⁺ + 3ADP + 3Pi → O₂ + 2NADPH + 3ATP  Cont.. Reactants: H₂O (water) NADP⁺ (nicotinamide adenine dinucleotide phosphate, oxidized form) ADP (adenosine diphosphate) Pi (inorganic phosphate) Products: O₂ (oxygen gas) NADPH (nicotinamide adenine dinucleotide phosphate, reduced form) ATP (adenosine triphosphate) ↂ 2. Dark reaction this is also known as light – independent stage, because it can occur in the absence of light as long as there is sufficient amount of H+ and ATP supplied from the light reaction. ↂ The dark reaction and enzymatic reaction H+ indirectly combines with CO2, in the stroma of chloroplast. ↂ The process is known as carbon fixation. Glucose (carbohydrate) is the immediate result of the dark reaction CONT… Summery Light Reaction 2H₂O + 2NADP⁺ + 3ADP + 3Pi → O₂ + 2NADPH + 3ATP Dark Reaction (Calvin Cycle) 6CO₂ + 12NADPH + 18ATP → C₆H₁₂O₆ (glucose) + 12NADP⁺ + 18ADP + 18Pi + 6H₂O Overall Photosynthesis 6CO₂ + 6H₂O + Light Energy → C₆H₁₂O₆ (glucose) + 6O₂  Transport in plant Brain storming question 1. How are different materials, such as water, mineral and food transported to and from different parts of the plant such as root, stem and leaf? 2. What are the routes of material transport in plants?  Mechanism of transport in plant Plants have two primary mechanisms for transporting substances within their bodies: 1. Xylem Transport: Function: Transports water and minerals from the roots to the leaves. Process: Root Hair Absorption: Water and minerals enter the root hairs through osmosis and active transport. Xylem Movement: The water and minerals are then transported through the xylem vessels, which are long, hollow tubes made of dead cells. Transpiration Pull: The evaporation of water from the leaves (transpiration) creates a pulling force that draws water up the xylem.  Theories and Hypotheses on the Mechanism of Transport in Plants Xylem Transport: Cohesion-Tension Theory: This is the most widely accepted theory. It proposes that water is pulled up the xylem by the tension created by transpiration, aided by the cohesive forces between water molecules and the adhesive forces between water and the xylem walls. Root Pressure Theory: This theory suggests that root pressure, generated by the active transport of ions into the root xylem, can contribute to water movement, especially at night. Phloem Transport: Pressure Flow Hypothesis (Mass Flow Hypothesis): This is the most widely accepted theory for phloem transport. It proposes that sugars are actively loaded into phloem sieve tubes at source tissues (like leaves), creating a high osmotic pressure. This pressure gradient drives the mass flow of sugar solution from the source to sink tissues (like roots or fruits).  Other Hypotheses and Ongoing Research: Polymer Transport Hypothesis: This hypothesis suggests that sugars are transported in the phloem in the form of large polymers, which can be more efficiently transported than individual sugar molecules. Active Transport in Phloem: While the pressure flow hypothesis is widely accepted, some researchers believe that active transport may play a role in phloem loading and unloading, especially in certain plant species or under specific conditions. Role of Phloem Proteins: Recent research has highlighted the importance of phloem proteins in regulating phloem transport. These proteins may play a role in phloem loading, unloading, and the maintenance of sieve tube structure Phloem Transport: Function: Transports sugars (produced by photosynthesis in leaves) to other parts of the plant for storage or use. Process: Phloem Loading: Sugars are actively transported into the phloem cells, increasing the solute concentration. Pressure Flow: The high concentration of sugars in the phloem creates a pressure gradient, causing the sugar solution to flow from areas of high pressure (source, like leaves) to areas of low pressure (sink, like roots or fruits). Phloem Unloading: Sugars are unloaded from the phloem into cells where they are needed. response in plants  Cont.. a tropism is the innate ability of an organism to turn in response to a stimulus. Non directional responses of plants to stimuli are called nastic movement Plants with a tropism will naturally turn toward a stimulus. A stimulus can be any signal from the environment, and individual tropisms are often named after the stimulus that causes the movement. In a positive tropism the plant will grow toward the stimulus.  Tropisms are growth movements in plants that occur in response to a stimulus. The direction of the response depends on the direction of the stimulus Examples of tropisms include Phototropism: plant growth in response to light Geotropism: plant growth in response to gravity Hydrotropism: plant growth in response to water Thigmotropism: plant growth in response to touch Chemotropism: plant growth in response to chemicals Thermotropism: A tropism that causes organisms to move towards a specific temperature. ↂ Tropism is exhibited by the shoot and root of a plant due to unequal concentration of growth hormone, commonly auxin, resulting in unequal growth ↂ Auxin, particularly Indole Acetic Acid (IAA), is plant growth hormone. ↂ It is produced at the tips of shoot and root. ↂ It is transported to the region of active growth and affects cell elongation, ↂ Shoot and roots respond differently to different auxin concentration. Auxins: Promote cell elongation and growth. Gibberellins: Stimulate stem elongation and seed germination. Cytokinins: Promote cell division and delay senescence. Abscisic Acid (ABA): Inhibits growth and promotes dormancy. Ethylene: Promotes fruit ripening and leaf abscission