Introduction

Herbs – Plants with green and tender stems and almost no branches. E.g: Tomato – Herb

Shrubs – Branches near the base, thin but hard stem. E.g: Lemon- shrub

Tree– Thick, brown stems. Tall with branches near the top. Mango – Tree. The branchy part of the tree above the stem is called the crown. Crowns of tall trees form a roof-like structure called Canopy. Crowns of smaller trees form a lower layer called Under-storey.

Creepers-plants with weak stems that spread on the ground or take support of other structures. [Money plants, beanstalk, gourd, grape vines]

Parts of a Plant

Stem – conducts water and minerals.

The part of a leaf by which it is attached to the stem – petiole.

The broad, green part of the leaf – lamina

Veins – lines present on the leaf. The thick line in the middle is midrib.

Design of veins – venation is of two types reticulate – net-like or parallel.

Transpiration – Leaves release water in the form of water vapor. The evaporation of water from leaves creates a suction that pulls water from roots to a greater height. It also cools the plant.

Plant Tissues

Xylem is the tissue in plants for the transportation of water and minerals. Food is transported by a second tissue called phloem. Xylem is made of tracheids, vessels, parenchyma, and fibers. Unidirectional movement is possible.

Phloem is also a complex permanent tissue like xylem and consists of sieve tubes, companion cells, parenchyma, and fibers. Transport food in both directions.

Photosynthesis

Photosynthesis – Leaves prepare food using carbon dioxide and water and the food produced is stored in form of starch. Oxygen is released in this process. The amount of oxygen released during photosynthesis is much higher than the CO2 that is released during nighttime.

The following things occur in photosynthesis, absorption of light energy by chlorophyll, conversion of light energy into chemical energy, and splitting of water molecules into hydrogen and oxygen. Reduction of CO2 into carbohydrates. These steps need not occur immediately.

Leaves take in CO2 from the atmosphere through pores present on surface called stomata; these are surrounded by guard cells. Leaves have a green pigment called chlorophyll that captures energy from the sun and uses it to synthesize food using water and CO2. Roots also take in air from the soil.

Types of food production in Plants

Cuscuta is a parasitic plant that takes nutrition from other host plants. The pitcher plant is insectivorous plant but it also carries out photosynthesis. These plant doesn’t get sufficient nutrition from the soil.

Fungi like yeast, Mushrooms are saprotrophs that feed on decaying matter.

Symbiotic relationship: Some organisms live together and share food and nutrients. [Lichens – Algae and fungus live together. Algae provide food by photosynthesis and fungi provide water, nutrients, and shelter. They are good indicators of pollution as they don’t grow in polluted areas. ]

[Rhizobium a bacteria converts atmospheric nitrogen into soluble form; this is absorbed by the leguminous plants that in turn provide it shelter and food. Thus nitrogenous fertilizers are not needed for leguminous plants. ]

Mycorrhizal fungi – Phosphorous fixing fungi lives in the roots of higher plants.

Frankia – nitrogen fixer bacteria for nonleguminous plants.

Blue-green algae, nostoc, azotobacter, and Lightning are also nitrogen fixers. Ammonia is converted to nitrites by nitro somas and nitrococcus. This is converted to nitrate by nitrobacteria.

Nitrate poisoning of groundwater causes methaemoglobina [blue baby syndrome].

Roots and their features

Roots- absorb water and nutrients from soil by a process called osmosis. They anchor the plant to the soil. Root hairs increase surface area for absorption.

Root types are tapped roots [the main root and lateral root] or fibrous roots [hair-like roots]. Some plants like banyan, grassroots arise from parts other than radicle called adventitious roots.

Plants with tap roots have reticulate venation and with fibrous roots have a parallel venation system.

Edible roots – carrot, radish, sweet potato, turnip, and tapioca.

Roots, stems, and leaves are vegetative parts of plants and flowers are reproductive parts of plants.

Plant Tissues

Two types of tissues in plants – permanent [non-growing] and meristematic [growing]. Depending on their location they are apical, intercalary or lateral. Initially, meristems grow cells the same as themselves but as these cells grow and mature they get differentiated into components of other tissues. Meristem cells have dense cytoplasm, no vacuoles, thin cell walls and large nuclei.

Permanent tissue is of multiple types like

Parenchyma – these are living tissues which store food and provide support to plants. They may contain chlorophyll and then it’s called chlorenchyma. In floating plants, it has air in the intercellular space and is responsible for buoyancy and called aerenchyma.

Collenchymas are living tissue that provides mechanical support to plants and also flexibility without breaking.

Sclerenchyma is dead tissue but hard and no intercellular space. It provides mechanical support to plant. Cell walls are thick due to lignin. The epidermis is the single, continuous layer of cells that covers the entire plant body. It has pores called stomata at certain points that allow gaseous exchange. Epidermis is thicker in plants in deserts to prevent water loss.

Plant Nutrients:

Macronutrients: These are present in plant tissue in large numbers; some are obtained from water [H, O], from the air [C], and the rest from soil [N, P, K, Ca, Mg, and S]. Useful as components of biomolecules, activate/inhibit enzymes, components of energy-related substances, affect the osmotic potential of cells,

Micronutrients: Needed in small amounts. These include iron, manganese, copper, molybdenum, zinc, boron, chlorine, and nickel.

The deficiency of N, K, and Mg are visible in senescent leaves as biomolecules with these elements are broken down to mobilize younger leaves. Boron and calcium deficiency lead to the death of meristem, buds, and tips. Phosphorous deficiency [blue leaves] and Fe, Mn, Mg, N deficiency [yellow leaves].

Miscellaneous

Green manures – cover crop that is planted on the field and ploughed under while it’s green. This is done to improve nutrients in the soil.

Legumes [N2 fixers] – cowpea, soybean,

Non legumes [add biomass, suppress weeds] – sorghum, millets, sudangrass, buckwheat

Cocaine is obtained from coca plant. Charas, ganja, hashish, and marijuana are obtained from cannabis. Opium, morphine, thebaine and heroin are obtained from the poppy plant.