Cell Organisation In Plants: ~organ And Systems In Plants ~regulating The Internal Environment

Cell Organisation in Plants ~Organ and systems in plants ~Regulating the internal environment

Cell organisation in plants • Plant organs such as leaves,stems and roots are formed from 2 main types of tissues: • a)meristemic tissues • b)permanent tissues • Meristemic tissues consist of small cells which have thin walls,large nuclei,dense cytoplasm & no vacoules. • Apical meristems located at the tips of roots and buds of shoots.~undergo mitotic cell division to increase number of cells for plant growth. • Lateral meristems are found in peripheral areas of stems and roots.

Permanent tissues • Permanent tissues consist of more mature cells that are either undergoing differentiation or have already undergone differentiation. • There are 3 types of permanent tissues: • a)epidermal tissue • b)ground tissue • c)vascular tissue

Characteristics and functions of permanent tissues. • • • • • • • •

Epidermal tissue Characteristics: The walls of epidermal cells which are exposed to air are normally covered by a waxy,waterproof coating called cuticle. Most epidermal cells are flat & have large vacoules. Functions: The cuticle helps prevent the loss of exercise water thru evaporation, protects the plant frm mechanical injury & prevents invasion disease causing microorganism. Some of the epidermal cells have long projections called root hairs.These structures increase the surface area for absorbtion of water & minerals. The lower epidermis contains specialised cells,called guard cells which surround the stomata.

Ground tissue • • • • • • • • • • • • • • • • • • •

Parenchyma tissue Characteristics: Consists of thin-walled cells which are loosely arranged. These cells are generally round & have large vacoules. Functions: Stores sugar and starch. The palisade mesophyll cells & spongy mesophyll cells contain chloroplasts & carry out photosynthesis. Also gives support & shape to plants. Collenchyma tissue Characteristics: Consist of elongated, polygonal cells which unevenly thickened cell walls. The cell walls are thickened by cellulose & pectin. Functions: An important source of support in herbaceous plant,young stems, leaf stalks, and petioles. Sclerenchyma tissue Characteristics: Rigid than collenchyma bcoz they have cell walls which are uniformly thickened by lignin. Fucntions: Supports & strengthens the plant body & provides protection to the plant.

Vascular tissue • • • • • • • • • • • • • •

Xylem tissue Characteristics: Consists of tracheids & xylem vessels. The cell walls of xylem are thickened with lignin which prevents food subs from entering the cells. When the cytoplasm disintegrates, a hollow tube is left behind. This feature allows water & minerals to flow easily thru the xylem vessels. Fucntions: Xylem conducts water & minerals frm the roots to the leaves. It provides support & mechanical strenght to plant. Phloem tissue Characteristics: Consists of parenchyma cells, sclereids,sieve tubes & companion cells. Fucntions: Transports organic substances such as carbohydrates & amino acids frm leaves to storage organs & to growing parts of plants.

Organs & systems in plants. • Ex of plant organs are leaves,stems,roots & flowers. • The root system is the absorptive system of a plant. • The roots are highly branced to absorb water & minerals frm the soil & transport them to the main vascular system(xylem). • The shoot system consists of organs such as stems,leaves,buds,flowers & fruits. • The leaves are made up of ground tissue,epidermal tissue,mesophyll tissue & vascular tissue. • They form the main photosynthetic system. • The reproductive system of plants consists of flowers which produce fruits & seeds after fertilisation has taken place.

Regulating the internal environment. • • • • • • • • •

Internal environment refers to the conditions tht exist within the body of an organism.particularly the composition of the interstitial fluid. The interstitial fluid fills the spaces btw the cells & constantly bathes the cells. The physical factors & chemical factors within the internal environment must be maintained at a relatively constant level. Physical factors: a)temperature,blood pressure,osmotic pressure Chemical factors: a)salt,sugar contents & pH Homeostasis is the maintanance of a relatively constant internal environment for the optimal functions of cells. The mechanism which governs homeostasis is called the negative feedback mechanism.