Topic 2: Plants Ch. 16,28 Characteristics of Plants p. 316 1. Multicellular eukaryotic organisms 2. Composed of tissues, organs and organ systems. 3. Cell walls made of cellulose. 4. Store energy as starch. 5. Contain photosynthetic pigments chlorophyll a and b. 6. Carry out alternation of generations. 7. Are adapted to life on land. Fig. 16.13 Where Did Plants Come From? p.316-318 The ancestor of plants is thought to be a group of green algae known as the Charophyceae. Both have green chlorophyll pigments, and the structure of their chloroplasts and chloroplast DNA are a close match. Fig. 16.5 Where Did Plants Come From? Sometimes algae are referred to as plants. Although both are often green, conduct photosynthesis, and are the base of many food chains, they are quite different. Plants have the following structures not found in algae: 1. Stomata Spaces that can be opened or closed to exchange gas. 2. Cuticle Waxy covering that prevents water loss. Where Did Plants Come From? 3. Lignin Protein used to make structures rigid for support. 4. Vascular tissue Used to transport materials and for support. 5. Gametangia Structure that protects gametes. Fig. 16.1 1
Terrestrial Adaptations pp.316-317 Life on Earth began in water. It took millions of years of evolution before plants could survive on land. On land, temperature ranges were extreme, there was wind and rain and air provides a lot less support than water. Terrestrial Adaptations Once on land, plants needed support to grow taller than their neighbours to receive the most light. Division of labour occurred with the development of tissues, organs and organ systems. Plant tissue can be divided into three types: Vascular Epidermal Ground Fig. 28.7 Vascular Tissue 610-611 Vascular tissue provides support and transports material within plants. It links the entire plant together and is found in all organs. Fig. 28.7 Vascular Tissue Vascular tissue contains cells joined in tubes that transport water and nutrients. There are two types: 1. Xylem Hollow, dead cells that transport water up the plant. 2. Phloem - Live cells that transport sugar down the plant. Fig. 28.11 How old is this plant? Which year did this tree grow the most? Why did it grow so much that year? Challenge 2
Dermal Tissue pp.610-611 Dermal tissue is a single layer of tightly packed cells that covers and protects all parts of the plant. Specialized dermal tissue in the roots called the epidermis is important for water absorption. It forms root hairs which increase the surface area for absorption. In other parts of the plant the epidermis produces a waxy cuticle which prevents water loss (desiccation). Ground Tissue pp.610-611 Most of the plant is ground tissue. It is responsible for most metabolic reactions e.g. photosynthesis, support, storage. Fig. 28.9 Fig. 28.8 Plant Organs pp.607-609,617 Plants can have up to two systems and four organs: 1. Root system (below ground) has roots as organs. 2. Shoot system (above ground) includes stems, leaves and flowers as organs. Each organ of a plant has the three tissues, which are continuous throughout the plant. The amount of each tissue present and the arrangement depends on the function of the organ. Fig. 28.1 Roots p.607 Roots grow in the dark soil so they can not photosynthesize. Roots absorb water and dissolved minerals through root hairs. They anchor the plant in harsh environments. They are more flexible than shoots because they are supported by soil. There are two basic forms of root systems in angiosperms: 1. Fibrous roots Shallow, large surface area, little anchorage. In monocots. 2. Taproot Deeper, less surface area, greater anchorage. In dicots. Fibrous Roots Tap root 3
Stems pp.608-609 Stems are part of the shoot system. Stems are located in the air and their primary function is for support. They have vascular tissue to transport water up (xylem) and sugar down (phloem) the plant. Lignin is present to provide support. Stems may have a waxy cuticle, hairs or bark to help prevent water loss. Modified Stem Structures 1. Runners - Horizontally growing stem that helps spread the plant. E.g. strawberries. 2. Rhizomes - Underground stem for anchorage and support. Roots usually grow from a rhizome. E.g. Fern Fig. 28.4 Modified Stem Structures 3. Tubers - Large circular structures that develop from rhizomes designed to store sugar and is also able to develop into a new plant. E.g. potato. 4. Tendril - Are threadlike structures that wrap around some other object giving the plant support as it climbs. E.g. pea. Fig. 28.4 Fig. 28.6 Leaves pp.608-611 Leaves are aerial organs used for photosynthesis and gas exchange. They have a cuticle for protection from desiccation, vascular tissue and stomata, which can be opened or closed, for gas exchange. Stomata are also used in transpiration. Transpiration- Water evaporates from the leaves in the top of the plant, drawing up water from the roots. Most photosynthesis occurs in leaves so they are thin and broad to be exposed to as much light as possible. Fig. 28.9 4
Flowers pp.324-326, 617 Flowers pp.324-326, 617 Flowers are made of modified leaves. Sepals are green and are the portion of the flower which encloses the bud before the flower emerges. Petals are brightly coloured to attract animals that will pollinate the plant. Carpel (or pistil) is the female part of the flower and is composed of the stigma (where pollen lands), ovary (where eggs are) and style (tube that connects the other structures. Stamen is the male part of the flower and is composed of the anther (makes pollen) and filament (supports the anther). Alternation of Generations pp.320-325 Life cycles of all plants feature alternation of generations. This means that plants have two body forms (or generations) which they alternate between. The two generations are sporophyte and gametophyte. Fig. 16.14 Alternation of Generations Sporophytes Diploid (2n) individuals that produce haploid spores by meiosis which grow by mitosis into gametophytes. Gametophytes Haploid (n) individuals that produce haploid gametes by with mitosis which fuse (fertilization) to form a diploid zygote which grows into the sporophyte. 5
Plant Groups After evolution from the charophytes, fossil records show four major periods of plant evolution: Mosses Ferns Gymnosperms Angiosperms Division Bryophyta pp.319-320 Evolved around 475 million years ago (Mya). Have no vascular tissue. No true stems, leaves, nor roots. Dispersed by spores. Have a dominant gametophyte. E.g. Mosses Fig. 16.7 Fig. 16.10 Fig. 16.9 Division Pterophyta p.321 Evolved around 400 Mya. Have vascular tissue. Have true stems, leaves, and roots. Dispersed by spores. Have a dominant sporophyte. E.g. Ferns Fig. 16.7 Division Coniferophyta p.322-323 Evolved around 360 Mya. Are also called gynmosperms (naked seed). Have vascular tissue. Have true stems, leaves, and roots. Dispersed by seeds. Have a dominant sporophyte. E.g. Black spruce Fig. 16.7 6
Division Anthophyta p.324-326 Evolved around 130 Mya. Also called angiosperm (covered seed). Have vascular tissue. Have true stems, leaves, and roots. Dispersed by seeds cover in a fruit. Have a dominant sporophyte. E.g. Rose Fig. 16.18 Angiosperm Reproduction pp.617-620 The male gametophyte is the pollen grain. It is produced in the anther and is transported to the stigma by the wind or an animal pollinator. Angiosperm Reproduction When pollen reaches the stigma, the plant is pollinated. The pollen grain then sends a tube down the style to the ovary of the flower. Sperm nuclei travel down the tube and enter the ovary. One fuses with an egg in the ovary fertilizing it. Each egg is inside an ovule inside the ovary. Each fertilized egg becomes a seed. The ovary then develops into a fruit. Fig. 28.23 Fig. 28.24 7
Monocots & Dicots p.606 Angiosperms can be divided into two groups: 1. Monocots Have one seed leaf. Their leaves have parallel veins and roots are fibrous. Monocots & Dicots p.606 2. Dicots Have two seed leaves. Their leaves have branching veins and tap roots. Fruit p.620 Fruit - A mature ovary that has been expanded after the ovules have been fertilized and the flower parts have withered. Fruit 1. Wind. E.g. Maple 2. Animals. E.g. berries Fig. 28.25 The function of fruit is to disperse the seed. This could be done by: 3. Water. E.g. Coconut 4. Propulsive. E.g. Lupin 8