All organisms that make their own food are called plants. Plant kingdom is grouped into four major phyta, namely.
- Thallophyta (bacteria, fungi, lichens and algae)
- Bryophyta (liverworts, hornworts and mosses)
- Pteridophyta (ferns)
- Spermatophyta (gymnosperms and angiosperms)
- Thallophyta includes fungi, Bacteria, lichens and algae.
- Algae can make their own food.
- Red algae is known as rhodophyceae.
- Green algae is known as chlorophyceae.
- Brown algae is known as phaeophyceae.
- Ulva is an example of a green algae. It is sometimes called sea lettuce.
- The study of fungi is called mycology.
- Chlorophyll is not present in fungi and remains as glycogen.
- The Fungi cell wall is made up of chitin.
- They are small plants and amphibians that grow densely together in moist and shady places.
- Sphagnum is a moss which occurs in bogs.
- The sphagnum moss is used as fuel and antiseptic.
- They are primitive vascular plants.
- They are mainly found in humid tropical regions.
- Angiosperms (flowering plants) : the seeds of these plants develop in an organ called the ovary in the flower.
- Gymnosperms (seed plant without flower) : gymnosperms include cycads, fir trees, pine trees, Cypress, spruce, ginkgo and redwood.
Structure of Plants
A plant has two organ systems which are the root system and the shoot system. The root system includes those parts of the plants such as leaves, buds, stems, flowers and fruits and The shoot system includes those parts of the plants below ground, such as tubers, roots, and rhizomes.
- The root system of a flowering plant begins its development from the hypocotyl of the embryo which gives rise to the primary root.
- Two kinds of root systems can be distinguished in flowering plants : tap root and adventitious root systems.
- Tap root system : the primary root grows vertically down into the soil. Later lateral or secondary roots grow from this at an acute angle outwards and downwards and from these other branches may arise.
- Adventitious root system : the primary root usually dies at an early stage and is replaced by numerous roots. These roots which develop from the stem are equal in size.
- The stem is ascending part of the main axis of the plant is developed from the plumule of the embryo, which lateral branches develop from axillary buds or from adventitious buds.
- Meristematic tissue : the meristematic cells present at the root and shoot apices divide mitotically and increase the length of the plant body.
- It is a temporary tissue.
- Apical meristematic : vertical growth.
- Lateral meristematic : side growth.
- Intercalary meristematic : nodal growth.
- Epidermis : the epidermis consists of a single layer of living cells which are closely packed.
- The walls are thickened and covered with a waterproof layer called the cuticle.
- Stomata with guard cells are found in the epidermis.
- In some stems either unicellular or multicellular hair like outgrowth, trichomes appear from the epidermis.
- It is situated to the inside of the epidermis.
- This region comprises the Collenchyma, parenchyma, and endodermis.
- Collenchyma : this tissue serves to strengthen the young stem.
- Parenchyma : beneath the Collenchyma cells are a few layers of thin walled cells, parenchyma with intercellular spaces.
- The synthesized organic food (mainly starch) is stored here.
- The intercellular air spaces are responsible for gaseous exchange.
- Endodermis or starch sheath : innermost layer of the cortex.
- The cells of this tissue store starch.
- It allows solutions to pass from the vascular bundles to the cortex.
Vascular Cylinders or stele
- This region comprises the pericycle, vascular bundles and pith (medulla).
- Pericycle : it is made up of sclerenchyma cells which are lignified, dead fibre cells these cells have thick, woody walls and tapering ends.
- It strengthens the stem.
- It provides protection to the vascular bundles.
- Vascular bundles : these are situated in a ring on the inside of the pericycle of the plant.
- The xylem provides a passage for water and dissolved ions from the root system to the leaves.
- The phloem are sieve tubes, companion cells. It provides food and minerals.
- Pith(medulla) : the pith occupies the large central part of the stem. It consists of thin walled parenchyma cells with intercellular air spaces.
- The medullary rays transport substances from the xylem and phloem to the inner and outer parts of the stem.
- This region is composed of small thick walled sclerenchyma on the inside of the epidermis. These layers of cells are followed by larger thin walled parenchyma cells.
- Sclerenchyma tissue strengthens the stem.
- Parenchyma tissue stores synthesised organic food such as starch.
- The leaf develops from the node and at least one bud is present in its axil.
- The foliage leaves are probably the most noticeable organs of a flowering plant.
- Leaves are adapted to perform certain important functions : photosynthesis, respiration and transpiration.
- Flower is a group of reproductive organs of the flowering plant.
- In a flower there are four types of structures called floral leaves. These are arranged in four whorls.
- Floral leaves are arranged on the swollen upper part of the flower stalk. The flower stalk is called pedicel and the swollen upper part is called thalamus.
Mineral deficiency in plants
|Calcium||Growing plant dies back, young leaves are yellow and crinkly|
|Iron||Young leaves are white or yellow|
|Magnesium||Older leaves have yellow in stripes between veins|
|Manganese||Younger leaves are pale with green veins|
|Nitrogen||Oldest leaves turn yellow and die permanently|
|Phosphorus||Older leaves have dead edges|
|Sulphur||Young leaves are yellow to white with yellow veins|
|Zinc||Young leaves are abnormally small; older leaves have many dead spots.|
Also Read :