Plants Chapters 23 and 24

Objectives Identify the major types of plant types Distinguish among the functions of the different types of plant types Identify the structures of roots, stems, and leaves Describe the functions of roots, stems, and leaves Identify the structures of a flower Examine the processes of seed and fruit formation and seed germination

Plant cells can be distinguished from animal cells by: Cell walls Central vacuole Contains chloroplasts

Dermal tissue of roots may have root hairs which are extensions of individual cells. These root hairs help the root absorb water and minerals.

Dermal Tissues A plant’s epidermis is composed of flattened cells that cover all parts of the plant. The epidermal cells produce the waxy cuticle that helps prevent water loss.

The stomata are openings in the cuticle of the leaf that controls exchange of gases. They are found on green stems and on the upper and lower surfaces of leaves. Cells called guard cells control the opening and closing of the stomata. This regulates the flow of water vapor from the leaf tissues.

Transpiration As a plant opens its stomata to release O 2 and take in CO 2, it loses water to the atmosphere. This occurs mainly through the leaves and stems

Cohesion As the water is evaporating through the stomata, the water is pulled up the plant by cohering (sticking together). You can simulate this by sticking the end of a paper towel in liquid – the liquid will transfer up the paper towel.

Translocation Is the movement of sugar and other organic molecules through the plant. This occurs through the phloem and moves across a concentration gradient.

Vascular Tissues Food, minerals and water are transported throughout the plant by vascular tissues.

Xylem is plant tissue composed of tubular cells that transports water and minerals from the roots to the rest of the plant. Phloem is the series of tubular cells that transport sugars and other organic compounds. These cells are alive at maturity. They are different because they do not have a nucleus or ribosomes.

Companion cells are nucleated cells that help manage the transport of sugars and other organic compounds The end walls between two sieve tube members are called sieve plates. The sieve plates have large pores that allow sugar and organic compounds to move from cell to cell. See 23.6 page 630

Meristematic Tissues Meristems are regions of actively dividing cells. They are small, spherical cells with large nuclei.

Apical meristems are found at or near the tips of roots and stems. They produce cells that allow the roots and stems to increase in length. Lateral meristems result in an increase in diameter. Vascular cambium produces new xylem and phloem cells in the stems and roots. Cork cambium produces a tough covering for the surface of stems and roots. The outer bark of a tree is produced by the cork cambium.

Ground tissue Their functions include photosynthesis, storage and support. The cells of ground tissue in leaves and green stems contain numerous chloroplasts that carry on photosynthesis.

Roots, Stems, and Leaves Roots are the underground parts of a plant. They anchor the plant in the ground, absorb water and minerals, and store food. The two main types of root systems are tap roots and fibrous roots.

The taproot is a central fleshy root with smaller branch roots. (carrots, beets) Used in moist areas.

Fibrous root systems have numerous roots branching from a central point. Used in dry/arid areas.

Roots have epidermis as their outer layer that includes root hairs that are extensions of the epidermal tissue. Just inside the epidermis is the cortex. This cortex tissue is involved in movement of water, minerals and food. Inside the cortex is the endodermis, a single layer of cells that forms a waterproof seal that surrounds the root’s vascular tissue. This is the layer that controls the flow of water and dissolved ions into the root. Inside the endodermis is the pericycle. The pericycle is a tissue that gives rise to lateral roots.

Leaves The main role of leaves is to trap the sun’s energy and perform photosynthesis. Some leaves are directly attached to the stem.

Other leaves are attached to a stalk called the petiole.

Leaf shape can be simple with a blade that is not divided.

Other leaf blades are compound in that their blade is divided into many leaflets. –Alternating – when only one leaf is present at each point –Opposite – when pairs of leaves are opposite each other

Monocots Monocots have: Leaves – parallel veins Cotyledon – one Vascular bundle – scattered Flowers – multiples of three

Dicots Dicots have: Leaves – usually netlike Cotyledon – two Vascular bundle – arranged in ring Flowers – multiples of fours or fives See page 641

Flowers and Flowering A flower is a complex structure directly involved in fertilization, pollination, and seed production.

A flower is usually made up of four kinds of organs: sepals, petals, stamens, and pistils.

Petals are leaflike, usually colorful structures arranged in a circle around the top of a flower stem. Sepals are also leaflike, usually green and encircle the flower stem beneath the petals.

Inside the circle of petals are the stamens. A stamen is the male reproductive structure of a flower. At the tip of the stamen is the anther; anthers produce pollen that contains sperm.

A complete flower is one that has all four organs. A flower that lacks one or more organs is called an incomplete flower. Do Problem-solving lab 24.2 See “Parts of a Flower” page 665

At the center of the flower lie one or more pistils. The pistil is the female structure of the flower. At the bottom of the pistil the area enlarges to form the ovary. The ovary contains one or more ovules, each containing one egg.

Annual – plants that only live for one year – petunias – zinnias – sunflowers Biennial – plants that live for two years – the second year they are flowering Perennial – plants that live for a long time. – azaleas – carnations

Nitrates are an important mineral in water because you can not make amino acids without it.