L.O 1Plant

structure and function

Group 2

Parenchyma Cells– They are the most abundant kind of plant cell. – They are found throughout the tissues of a plant.– These spherical cells have thin, flexible cell walls. – Most parenchyma cells usually have a large central

vacuole, which sometimes contains a fluid called sap. – The fleshy parts of most fruits are made up mostly of parenchyma cells.

– When the cells contain chlorophyll, they can carry photosynthesis and are called chlorenchyma.

– Functions:

food production (photosynthesis) so it can contain numerous chloroplasts -- storage of water and nutrients --healing.

Collenchyma Cells

– They are long cells with unevenly thickened cell walls.

– These cells are arranged in tube-like strands or cylinders that provide support for surrounding tissue.

– There usually grouped in strands.

– Celery stalks contain a great amount of collenchyma cells.

Function:

It allows the cells to grow. The walls of collenchyma cells can stretch as the cellsgrow while providing strength and support.

 Can carry photosynthesis if chlorophyll is present.

Sclerenchyma Cells:

– The walls of sclerenchyma cells are very thick and rigid.– At maturity, these cells often die.

– Although their cytoplasm disintegrates, their strong, thick cell walls remain and provide support for the plant.

–  Present in the vascular bundles in xylem and phloem in stem, roots and in the veins of leaves.  present Also, present in the hard seed coat covering.

Cells are dead but are connected through the pits, pits are places where lignin is absent.

Kinds of Sclerenchyma cells:

1) Fibers:

Fibers are long, thin cells that form strands.

They provide support and strength for the plant and are the source of fibers used for making linen and rope.

A type of fiber is associated with vascular tissue

2) Sclerids:

Sclerids are irregularly shaped and usually found in clusters. They are the gritty texture of pears and a major component of the pits found in peaches and other fruits.

Dermal Tissue System:– It forms the outside covering of plants (epidermis).

– It is made of parenchyma cells.– The outer epidermal wall is often covered by a waxy layer called

Cuticle, which prevents water loss.– Some epidermal cells of the roots develop

hair-like extentions (Trichomes) that increase water absorption.

– In some cases, trichomes are glandular and secrete toxic substances that help protect the plant from predators.

Dermal Tissue System:

– It has Stomata (openings in the leaf and system epidermis) which regulate the passage of gases and moisture into and out of the plant.

– In woody stems and roots, the epidermis is replaced by dead cork cells.

Ground Tissues:Ground tissue makes up much of the interior of a plant and carries out basic metabolic functions. Ground tissue in stems provides support and may store food or water. Ground tissues in roots may also store food.

Function: metabolism, storage, and support activities

a) the ground tissue of the leaf (called mesophyll) uses the energy in sunlight to synthesize sugars in a process known as photosynthesis

b) the ground tissue of the stem (called pith and cortex) develops support cells to hold the young plant upright

c) the ground tissue of the root (also called cortex) often stores energy- rich carbohydrates

Vascular Tissues:– Vascular tissue runs through the ground tissue inside a plant. Your body was able

to grow from a single cell to perhaps 100 trillion cells because, 21 days after fertilization, a tiny heart began to pump blood throughout your tiny self – and it hasn’t stopped since. The blood it pumps carries water, oxygen and nutrients to each one of your trillions of cells, and removes CO2 and other wastes.

– Of course plants don’t have hearts, but they do have vessels that transport water, minerals, and nutrients through the plant. These vessels are the vascular tissue, and consist of xylem and phloem. Xylem and phloem are packaged together in bundles.

– Function: the transport of water and dissolved substances inside the plant

– Tracheids and vessel elements are the conducting cells of the xylem. These cells die when they mature but their cell walls remain.

– Tracheids are tubular cells tapered at each end. The cell walls between adjoining tracheid have pits through which water and dissolved minerals flow.

– Vessel elements are tubular cells that transport water throughout the plant. They are wider and shorter than tracheids and have openings in theirend walls.

– Anthophyte vessel elements are thought to transport water more efficiently than tracheids because water can flow freely from vessel element to vessel element through the openings in their end walls.

– Phloem is made up of tubular cells joined end to end.– It is similar to xylem because phloem also has long cylindrical cells. However these

cells, called sieve tube members are alive at maturity.– They contain cytoplasm but do not have a nucleus or ribosomes. – Next to each sieve tube member is a companion cell. Companion cells are nucleated

cells that help with the transport of sugars and other organic compounds through the sieve tubes of the phloem.

– The end walls between two sieve tube members are called sieve plates.

– The sieve plate have large pores that allow sugar and organic compounds to move from sieve tube member to sieve tube member. Phloem can transport materials from the roots to the leaves also.

– a) the xylem carries water and dissolved ions from the roots to stems and leaves

– b) the phloem carries dissolved sugars from the leaves to all other parts of the plant

– Summary• The three types of plant cells are found in each of the major types of

plant tissues: dermal, ground, and vascular tissues.• Dermal tissue covers the outside of a plant in a single layer of cells

called the epidermis. It mediates most of the interactions between a plant and its environment.

• Ground tissue makes up most of the interior of a plant. It carries out basic metabolic functions and stores food and water.

• Vascular tissue runs through the ground tissue inside a plant. It consists of bundles of xylem and phloem, which transport food, water and minerals throughout the plant.

Meristematic tissues

Apical Meristems Lateral Meristems

Vascular Cambium Cork Cambium

Intercalary Meristems

Plant growth originates mainly in Meritesm, regions where cells continuously divide.1) Apical meritesm: It is located at the tips of stems and roots. Most of plants grow in length through apical meritesm.

2) Intercalary Meritesm: It Is located above the bases of leaves and stems. Some monocots grow in length through Intercalary meritesm. It allows grass leaves to quickly regrow after being grazed or mowed.

Gymnosperms and most dicots also have Lateral Meritesms, which allows stems and roots to increase in diameter. It is located near the outside of stems and roots. It has two types:1) Vascular Cambium2) Cork Cambium

1) Vascular Cambium: It is located between xylem and phloem. It produces additional vascular tissues.

2) Cork Cambium:• It is located outside the phloem.• It produces cork cells which replace

epidermis in woody stems and roots.• Cork cells are dead cells that provide protection and prevent water loss.

So, the tree grow taller and wider over time.

Note:– A third type of lateral meristem is found in

grasses, corn, and other monocots. This meristem adds cells that lengthen the part of the stem between the leaves. These plants do not have a vascular or a cork cambium.

Group 21-Salah Ayman2-Mahmoud Ibrahim3-Mina Magdy4-Kiroulls Youssef5-Islam Essam