SBI3U PLANTS UNIT NOTES

14.1 Plant Organs, Tissues, and Cells

Saad, Asim, Jerrol, Yasean

04/08/2023 01:33:39 AM

Why are you looking here?! Look at the information, fool. 2

Plant Organs

The primary organ systems of a plant are the roots, shoots, leaves and flowers

There are two groups of angiosperms: dicotyledons, and monocotyledons. Monocotyledons (or monocots) contain species with long, thin leaves such

as grasses, orchids, and lilies Dicotyledons (or dicots) are the larger group, containing broad-leaf species

such as dandelions, canola, and maple trees.

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Root Systems

Roots are structures that anchor a plant in the soil, absorbing minerals and water, and providing structural support Monocots have fibrous root systems consisting of a mat of thin roots

spread out below the soil surface, in order to provide increased exposure to soil nutrients and water.

Dicots have a tap-root system with one large vertical root with many small branches

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Root Systems (cont.)

Although most roots are below ground, some roots have special adaptions to the plant’s environment For example, buttress roots form on some tall or shallowly rooted tree

species to help support them above ground.

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Shoot Systems

Shoots are above-ground structures consisting of stems, leaves, and flowers.

Stems are the parts of a plant that support leaves and flowers They play an important role in transporting materials in a plant. Vascular tissue runs vertically in the stem, and it transports water and

minerals from the roots up to the leaves, and the food the plant creates to wherever its needed.

Nodes are the points on the stem at which leaves are attached, and internodes are the portions of the stem between nodes

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Shoot Systems (cont.)

Due to their wide range of modified roles, shoots vary considerably in their appearance. The stems of cacti are specialized to store water and potatoes are swollen shoots to

store starch. Undeveloped shoots are called buds

Terminal buds are found at the tip of stems, whereas axillary buds are found in the angles (axils) formed by a leaf and the main stem.

Growth from such axillary buds forms the plant’s branches.

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The Leaf

Leaves are the primary food manufacturing sites of a plant They capturing sunlight and convert it to chemical energy during

photosynthesis. The main part of the leaf is the blade

A stalk, called a petiole connects the leaf to the stem The veins that run through are made of vascular tissue and support

tissue, and carry water and nutrients into the leaf The venation is the arrangement of veins in the leaves. Monocots have several major veins that run parallel along the blade,

and dicots have a branching network of veins.

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Flowers and Sexual Reproduction

Flowers contain 4 different rings of modified leaves that are called sepals, petals, stamens, and pistils Sepals protect the flower bud, petals are colourful to attract pollinating insects,

Stamens are the male reproductive structures, and the pistils are the female reproductive structures.

Each Stamen consists of a long stalk topped by a sac called an anther, in anthers meiosis creates spores that develop into pollen grains

There exits an ovary at the base of each pistil is an ovary, in each ovary is an ovules.

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Seed Development

After fertilization takes place, the ovule develops into a seed The interior of the seed is protected by a tough outer coat called a

seed coat In the seed there is …

The endosperm, which is the food source for the developing embryo. It contains starches, proteins and oils

The embryo is a miniature root and shoot taking form The cotyledon is a embryonic leaf which delivers and stores nutrients for

the embryo

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Seed Dispersal

After many cycles of mitosis, the development of the embryo is suspended and is dispersed by the parent plant.

In this stage the seed is dispersed from the parent plant In many flowering plants, a fruit is developed from the ovary of an

angiosperm Fruits protect the seeds from the parent plant

Seed dispersal happens in many ways Sticking onto an animals fur In fruits for animals to digest

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Seed Germination

The seed embryo can grow, this is called germination Some plants have specific requirements for this to happen After breaking out of the seed coat the journey of the plant shoot

through the soil is difficult Plants have adaptations to protect the shoot as it grows toward the

surface

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Vegetative Reproduction

Plants are capable of asexual reproduction (known as vegetative reproduction). Vegetative reproduction results in genetically identical offspring. It can be done either naturally or with human help

An example of natural vegetative reproduction is how strawberry plants send out runners to form “clone” offspring.

The simplest way to clone a plant is to cut off a leaf or stem and place the cut end in water or soil.

The cells at the cut end of the petiole or stem become undifferentiated and then form new plant tissues and organs.

In many woody species, a branch from one plant can be “grafted” onto the stem of another plant belonging to the same or a closely related species.

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Tissue Systems

Plants have three main tissue systems: dermal, vascular, and ground tissue systems.

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Tissue Systems –Dermal Tissue

Outer covering or “skin” of the plant The epidermis is the dermal tissue of non-woody organs.

Composed of one or more layers of cells Covers and protects all the young parts of the plant Some epidermis is specialized

Ex/ the epidermis of leaves and stems secretes a waxy cuticle to help the plant retain water, whereas many species have epidermal hairs to trap or poison insects to protect the plant from pests.

Pores called stomata are located in the epidermis of leaves and some other tissues for gas and water exchange between the environment and the interior of the plant.

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Tissue Systems –Vascular Tissue

Transports water, mineral nutrients, and organic molecules between roots and shoots.

Contributes to the structural support of the plant Two types of vascular tissue: xylem, and phloem

Xylem transports water and dissolved minerals upward from the roots to the shoots

Phloem transports food made in leaves to roots and the parts of the shoot system that require the energy.

Located in the centers of roots, but arranged in many separate strands called vascular bundles in stems. Monocot stems have vascular bundles scattered throughout tissue Dicot stems have vascular bundles arranged in a ring

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Tissue Systems –Ground Tissue

Fills spaces between dermal and vascular tissues Makes up majority of young, non-woody plants and functions in

photosynthesis in the shoot and in storage and support throughout the plant.

The ground tissue of the root consists mainly of a mass of cells called the cortex.

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Types of Plant Cells

Three basic cell types in plant tissues: parenchyma, collenchyma, and sclerenchyma.

Parenchyma cells: Made up of thin cells walls, and large central vacuoles. Perform variety of functions, including food storage, photosynthesis, and

cellular respiration. Fruits are mostly made up of parenchyma cells Food-conducting cells of phloem are also parenchyma cells. Most abundant type of cell

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Types of Plant Cells (cont.)

Collenchyma cells: Unevenly thickened cell walls Grouped in strands or cylinders Provide support in growing parts of the plant Found below the surface of young stems and petioles Elongate with the stems and leaves they support as they grow

Sclerenchyma cells: Specialized cells for support Grow and then die within a mature part of a plant Become most useful when dead

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Types of Plant Cells (cont.)

The lignin-rich cell walls are left behind in the dead cells, creating a “skeleton” that supports the plant.

The water conducting cells of xylem are specialized sclerenchyma cells No particular type of plant tissue is made up of just one type of cell,

the cells work together to form tissues.

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Cellular Structure of a Leaf

Leaves are designed to capture sunlight and allow gas exchange between the surrounding air and the cells inside the leaf that carry out photosynthesis.

The upper and lower surfaces are covered with epidermal cells These cells are covered by a waxy cuticle, in order to reduce the amount of

water the leaf looses. The epidermal layer on the lower surface of the leaf contains stomata

flanked by guard cells Guard cells open and close the stomata, to control the diffusion of gases in and

out the leaf.

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Cellular Structure of a Leaf (cont.)

The ground tissue of the leaf is made of mesophyll, a parenchyma cell specialized for gas exchange. Dicots have two layers of mesophyll cells.

Under the upper epidermis is a layer of elongated palisade mesophyll cells specialized for capturing light energy and carrying out photosynthesis.

Above the lower epidermis is a layer of loosely packed spongy mesophyll cells (also called aerenchyma) to allow carbon dioxide and oxygen to circulate within the leaf.

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SBI3U PLANTS UNIT NOTES