Kingdom Plantae Biology 2201 6.1 6.2 : A Brief Survey of Plants The study of plants is called botany. Plants are believed to have evolved from green algae. The main plant (land) characteristics are as follows: 1. Common cellular structures: all are eukaryotes multicellular cell wall composed of cellulose chlorophyll contained in chloroplasts produce starch as carbohydrate food reserve central vacuole 2. Photosynthetic organisms: autotrophs / producers 1
3. Most are stationary. 4. Reproduction occurs through a life cycle called alternation of generations. The cycle consists of two generations: (a) Sporophyte generation reproduces asexually (b) Gametophyte generation reproduces sexually The advantage of alternation of generations is the combined advantage of sexual and asexual reproduction. Asexual only one parent needed Sexual produces much genetic variety 2
Classification of Plants There are two major groups of plants. They are classified according to the presence or absence of vascular tissue. Vascular tissue is a special tissue for support and for the transport of materials within the plant. There are two forms of vascular tissue: Xylem: This transports water and minerals up the stem of the plant into the leaves. Phloem: This transports glucose produced by the leaves, during photosynthesis, down the stem and into the roots. 3
The two groups that plants are divided into: 1. Non Vascular: These include mosses (Bryophytes), liverworts (Hepatophytes), and hornworts (Anthocerophytes). These plants do not possess vascular tissue. They are short plants that usually grow in areas that have a good supply of water. The gametophyte generation is dominant. 2. Vascular Plants (Tracheophytes): These include horsetails, ferns, gymnosperms, and flowering plants (angiosperms). They have well developed vascular tissue. The sporophyte generation is dominant. 4
biology 2201 ch 6 notes plants.notebook Bryophyte (moss) Tracheophyte Gymnosperm (fir tree) 5
biology 2201 ch 6 notes plants.notebook Tracheophyte Angiosperm (fruit bearing) Tracheophyte Angiosperm (flowering) 6
Non vascular Plants (i) Lack vascular tissue. This accounts for the remaining characteristics. (ii) Lack true roots, stems, or leaves. (iii) Small in size, growing close to the ground (1 5 cm) (iv) Restricted to moist environments (bogs, etc) (v) Transitional group between aquatic and terrestrial plants. (vi) Major forms include moss, liverwort, and hornwort. 7
Non Vascular Adaptations for Life on Land 1. Water Conservation waxy waterproof covering called a cuticle or cutin found on leaflets 2. Gas Exchange pores found on the top of the leaflets 3. Internal Transport occurs by diffusion, no vascular tissue 4. Internal Support none 5. Water Absorption small filaments called rhizoids 6. Reproduction dependent upon water to move sperm to the egg Moss Life Cycle 8
Life Cycle of a Moss cont. Non vascular plants have no xylem and phloem, and need water for fertilization (sperm must swim to egg). Hence they are found in moist, shaded areas like bogs or at the bases of trees. As well, the gametophyte generation is dominant. Male gametophyte develops antheridium (produces sperm) Female gametophyte develops archegonium (produces egg) Tracheophytes (i) Possess vascular tissue (xylem and phloem). This accounts for the remaining characteristics (ii) Possess true roots, stems, and leaves. (iii) Large in size, growing well above the ground. (iv) Not restricted to moist environments; well distributed over the Earth s surface. Can even exist in areas where water is scarce. (v) Most complex group of plants. (vi) Major forms include: vascular spore dispersing plants: plants like ferns, horsetails, club mosses, and whisk ferns that spread spores to reproduce vascular seed dispersing plants: the most dominant and successful group of plants. These organisms produce seeds and are also divided into 2 groups gymnosperms: cone bearing plants angiosperms: flowering plants 9
Trachoephyte Adaptations for Life on Land 1. Water Conservation cuticle or cutin present on leaves. 2. Gas Exchange pores called stomata found on the bottom of leaves. 3. Internal Transport contains vascular tissue 4. Internal Support vascular tissue 5. Water Absorption system of roots is present 6. Reproduction water is not required for movement of sperm to egg except in the case of ferns. In gymnosperms and angiosperms, sperm is contained inside a pollen grain that is moved by wind and insects. Stomata are better for gas exchange for the following reasons: (1) No holes in the waterproof covering. (2) In the shaded area of the leaf (less water loss). (3) They won t become clogged by dust and other materials. Gas Exchange 10
biology 2201 ch 6 notes plants.notebook Tracheophyte (fern) Tracheophyte (fern) 11
Vascular Spore Dispersing Plants Ferns (see life cycle, p. 173) ferns produce spores, like moss sporophyte generation dominant (unlike moss) ferns have true roots, stems, and leaves and vascular tissue the gametophyte generation is called the prothallus. Both male and female structures are found on the prothallus. Male antheridium Female archegonium Vascular Seed Plants Gymnosperms and Angiosperms 12
Vascular Seed Plants Vascular seed plants have three successful adaptations that contribute to their success on land: (1) gametophytes of seed plants become even more reduced. They are kept within the moist reproductive tissue of the sporophyte generation rather than developing in the soil as an independent generation living outside. (2) Pollination by wind (or other means) replaces swimming as the mechanism for delivering sperm to eggs. (3) The seed. Instead of the zygote plant developing directly into a sporophyte and fending for itself, it develops into an embryo with a food supply encased in a seed coat. The coat protects the embryo from drought, cold, and other harsh conditions. Seeds also help in dispersal. 2 groups of vascular seed plants: (1) gymnosperms (2) angiosperms Gymnosperms (Conifers) include evergreen trees (pine, spruce, fir, cedar, redwood) instead of flat leaves, gymnosperms have needles which reduce water loss seeds of gymnosperms are exposed on cones and are dispersed by wind Life cycle of a gymnosperm male cones make microspores that develop into pollen grains (male gametophytes). Female cones develop ovules when pollen grains land on female cones, they produce a pollen tube that grows into the tissue of the female gametophyte and begins to tunnel towards the egg. Two sperm cells travel towards the egg, but one dies along the way while the other fertilizes the egg. 13
Life cycle of a gymnopserm Angiosperms Angiosperms are the most diverse plant group on Earth. They live in every habitat where plants may be found. The main reasons for their success include: (1) well developed root, stem, and leaf structures with vascular tissues for conduction of food, water and nutrients. (2) A waxy cuticle covered by cutin and special pores (stomata) in their leaves that can close to prevent water loss (3) Pollination that eliminates the need for water for reproduction, and additional pollen dispersal methods besides wind, such as mutualistic relationships with animals. (4) The formation of seeds by a process of double fertilization which results in a large food store, fruit that protects seeds, and adaptations or mechanisms that enable effective seed dispersal fruit covering the seed aids in dispersal. Animals will eat the fruit and drop the seeds, or the seeds will pass through their digestive systems 14
The Flower The flower is the reproductive structure of an angiosperm Parts of the flower: (1) sepals a group of modified leaves that encloses and protects the flower bud before it opens (2) petals brightly coloured structures of flowers used to attract insects. (3) Stamen the pollen producing male reproductive organ of a flower; consisting of an anther (makes pollen) and filament (the stalk) (4) Pistil the female reproductive organ of the flower, consisting of a stigma (receives pollen grain), style (leads to the ovary) and ovary (contains the egg developing ovules) Flower & Seed Structure 15
Life Cycle of an Angiosperm immature gametophytes are produced by the anther as pollen grains; female gametophytes are produced in ovules, which also contain an embryo sac with eight nuclei (one egg) once the pollen is released, it gets carried to the pistil and sticks to the stigma the pollen grain germinates and extends a tube that grows down the style of the pistil (like in gymnosperms) once the pollen tube reaches the ovary, it penetrates through a pore in the ovary and discharges two sperm cells. One sperm cell unites with the egg to form a diploid zygote. The other sperm cell fuses with two nuclei of the embryonic sac. This process is called double fertilization. after double fertilization, the ovule matures into a seed, and the other fertilized structure divides repeatedly to produce endosperm, which is rich in starch reserves as is used by the embryo as food. The ovary of the female develops into the fruit. Life Cycle of an Angiosperm 16
Seed dispersal adaptations Angiosperms can have several adaptations which aid in seed dispersal, including: (1) animals can help pollinate flowers pollen can stick to animal fur and transported from flower to flower insects like bees help pollinate flowers by transporting pollen from pollen to pollen seeds of flowering plants are not usually digestible by animals. Once animals eat fruit, the seed passes through unhurt (2) some seeds have special modifications like wings that help in wind dispersal Groups of Angiosperms There are 2 major groups of angiosperms: 1. monocotyledons (monocots) 2. dicotyledons (dicots) 17
Monocots vs Dicots 18