Plant Biology Assessment PDF

Life sciences 2 Plant biology Assessment Lecture 1 Growth: is the increase in mass that results from cell division and cell expansion. Development: Is the sum of all the changes that progressively elaborate an organism's body. Intermediate growth: Means that they grow for as long as they live Deter...

Life sciences 2 Plant biology Assessment Lecture 1 Growth: is the increase in mass that results from cell division and cell expansion. Development: Is the sum of all the changes that progressively elaborate an organism's body. Intermediate growth: Means that they grow for as long as they live Determinate growth: Means that they grow until a certain point or age. Annuals: Plants that complete their life cycle, from germination, through flowering and seed, production to death, in a single year or less. Biennials: Plants that live for 2 years, often there is an intervening cold period between the vegetative growth season and the flowering season. Perennials: Plants that live for many years including trees, shrubs and some grasses. Meristems: Its where cell division occurs, in plants to make it wider or taller. Apical meristems: is located at the tips of the roots and the buds of shoots, supply cells for the plant to grow in length -​ Primary growth: enables roots to ramify through the soil and shoots to extend their exposure to light. In woody plants, primary growth is restricted to the youngest parts of the plant, like the tips of the roots and shoots. -​ Secondary growth: progressive thickening of roots and shoots. Lateral meristems: It becomes a secondary growth from lateral meristems, cylinders of dividing cells extending along the length of roots and shoots. The lateral meristems develop in slightly older regions of the roots and shoots. Primary plant body: Primary growth produces the primary plant body- the parts of the root and shoot system produced by apical meristems. -​ The Roots: The root is covered by a thimble like root cap, which protects the meristem as the root pushes through the abrasive soil during primary growth. The cap also secretes a lubricating slime. Growth in length is concentrated near the root’s tip, where three zones of cells are located. -​ Zone 1: Zone of cell division- Includes the apical meristem and its derivatives, primary meristems. The apical meristem produces the cells of the primary meristems and also replaces cells of the root cap that are sloughed off. Near the middle is the quiescent center, cells that divide more slowly than other meristematic cells. These cells are relatively resistant to damage from radiation and toxic chemicals. They may act as a reserve that can restore the meristem if it becomes damaged. -​ Zone 2: Zone of elongation- Where cells elongate, sometimes to more than 10 times their original length. It is this elongation of cells that is mainly responsible for pushing the root tip including the meristem ahead. The meristem sustains growth by continuously adding cells to the youngest end of the zone of elongation  -​ Zone 3: Zone of maturation- Cells begin to specialize in structure and function. In this root region, the three tissue systems produced by primary growth complete their differentiation, their cells becoming functionally mature. Three primary meristems give rise to the three primary tissues of roots: Dermal tissue: Epidermis (rhizodermis) Ground tissue: Cortex with endodermis Vascular tissue: Xylem and phloem Root vascular structure: Dicots: The xylem cells radiate from the center of the stele in two more spokes with phloem developing in the wedges between spokes. Monocots: The pith of the stele is generally ringed by vascular tissue with alternating patterns of xylem and phloem. Shoot growth Shoot apical meristem at terminal bud: Is a dome-shaped mass of dividing cells at the terminal bud. It forms the primary meristems- protoderm, procambium and ground meristem. Leaves arise as leaf primordia on the flanks of the apical meristem. Axillary buds develop from islands of meristematic cells left by apical meristems at the leaf primordia base. Leaf primordia develop from mersitem: Within the bud, leaf primordia are crowded close to tg because internodes are very short. Most elongation of the shoot occurs by growth in length of slightly older internodes below the shoot apex. This growth is due to cell division and cell elongation within the internode. In some plants, particularly grasses, internodes continue to elongate all along the length of the shoot over a prolonged period. Axillary buds give rise to branches: Have the potential to form branches of the shoot system at some later time. While lateral roots originate from deep in the main root, branches of the shoot system originate from axillary buds, at the surface of a main shoot. Because the vascular system of the stem is near the surface, branches can develop with connections to the vascular tissue without having to originate from deep within the main shoot. Unlike their central position in a root, the vascular tissue runs the length of a stem in strands called vascular bundles. At the cone of root and shoot connection, the stem’s vascular bundles converge as the root’s vascular cylinder. Each vascular bundle of the stem is surrounded by ground tissue. Stem vascular bundles Dicots: The vascular bundles are arranged in a ring, with pith on the inside and cortex outside the ring. The vascular bundles have their xylem facing the pith and their phloem facing the cortex. Thin rays of ground tuíssue between the vascular bundles connect the two parts of the ground tissue system, the pith and cortex. Monocots: The vascular bundles are scattered throughout the ground tissue rather than arranged in a ring. Leaf structure Epidermis: Is composed of cells tightly locked tg like pieces of a puzzle in both sides of the leaf. The leaf epidermis is a first line of defense against physical damage and pathogenic organisms and the waxy cuticle is a barrier to water loss from the plant. Stomata: The epidermal barrier in leaves is interrupted only by stomata, tiny pores flanked by specialized epidermal cells called guard cells. Each stomata is a gap bw a pair of guard cells. The stomata allow gas exchange bw the surrounding air and the photosynthetic cells inside the leaf. They are also the major avenue of evaporative water loss from the plant- a process called transpiration. Leaf internal tissue Mesophyll: The ground tissue of the leas is the mesophyll, is sandwiched bw the upper and lower epidermis. It contains mainly parenchyma cells equipped with chloroplasts and specialized for photosynthesis. (Carbon dioxide and oxygen circulate through the labyrinth of air spaces around the irregular spaced cells. The air spaces are particularly large near stomata, where gas exchange with the outside air occurs) Vascular tissue in leaves Xylem: Brings water and minerals to the photosynthetic tissues. Phloem: the phloem carries its sugars and other organic products to other parts of the plant. The vascular tissues also impact the shape of the leaf. Secondary Growth overview The stems and roots, but not all the leaves, of most dicots increase in girth (omkrets) by secondary growth. The secondary plant body consists of the tissues produced during this secondary growth in diameter. -​ The vascular cambium acts as a meristem for the production of secondary xylem and secondary phloem. The vascular cambium is a cylinder of meristematic cells that forms secondary vascular tissue. The accumulation of this tissue over the years accounts for most of the increase in diameter of a woody plant. Secondary xylem forms to the interior and secondary phloem to the exterior of the vascular cambium  -​ The cork cambium acts as a meristem for a tough thick covering for stems and roots that replaces the epidermis. It produces cork. -​ Secondary growth continues over the years, layer upon layer of secondary xylem accumulates, producing the tissue we call wood. Formation of wood and growth rings Early wood (spring): The first tracheid and vessel cells formed in the spring have larger diameter and thinner walls than cells produced later in the summer. The structure of the early wood maximizes delivery of water to new, expanding leaves. Late wood (summer): The thick walled cells of later wood provide more physical support. This pattern of growth: cambium dormancy, early wood production, and late wood production, each year produces annual growth rings. Cork structure/ lenticels Cork cambium produces cork cells, which accumulate at the cork cambium’s exterior. Waxy materials deposited in the cell walls of cork cells before they die acts as a barrier against water loss, physical damage and pathogens. The cork and phelloderm produced by cork cambium and cork cambium itself forms the periderm, a protective layer that replaces the epidermis. In areas called lenticels, splits develop in the periderm because of higher local activity of the cork cambium. These areas within the trunk facilitate gas exchange with the outside air. Bark structure Refers to all tissues external to the vascular cambium, including secondary phloem, phelloderm, cork cambium and cork. Only the youngest secondary phloem functions in sugar transport. Older secondary phloem dies and helps protect the stem until it is sloughed off as a part of the bark during later season of secondary growth. After several years of secondary growth, several zones are clearly visible in a stem. These include two zones of secondary xylem, the vascular cambium living secondary phloem, cork cambium, and cork. Root secondary growth Older parts of the roots, with secondary growth function mainly to anchor the plant and to transport water and solutes bw the younger roots and the shoot system. Over the years, as the roots become woodier, annual rings develop and tissues external to the vascular cambium form a thick bark. Old stems and old roots are quite similar. Lecture 2 Life cycle of a plant Stages: Germination → Growing plant → Flowering → Pollination → Fertilization → Seed dispersal Sexual reproduction: Production of sex gametes followed by their fusion and the development of an embryo. Asexual reproduction: Vegetative growth. Portion of the plant is taken from the mature sporophyte and used to create a brand new plant. This results in a genetically identical progeny. This is an advantage if the plant shows superior qualities. Or a disadvantage because there is no genetic variability which is crucial for the health of the plant as a species. Angiosperm life cycle Male gametophyte: Filament and anther builds up a stamen. Microspores (pollen) Female gametophyte: Stigma, style and ovary builds up a carpel. Megaspores (embryo sac) Pollination Process: In angiosperms, pollination is the transfer of pollen from an anther to a stigma. Process of pollination requires pollinators- agents that carry or move pollen grains from the anther to the stigma of the carpel. Flower traits that attract different pollinators are known as pollination syndromes. Ways to pollinate the stigma: -​ Wind -​ Water -​ Insects -​ Animals Biotic pollination (Pollination by animals) : 80% of all pollination is biotic -​ Entomophily: Pollination by insects ex. bees, wasps, ants, beetles, moth and butterflies -​ Zoophily: pollination by animals ex. birds and bats Abiotic pollination (pollination by non-animal factors): -​ Anemophily: Pollination by wind (98% of abiotic pollination) -​ Hydrophily: Pollination by water (aquatic plants) Outcome: Successful pollination leads to the generation of pollen tube, the discharge of sperm and the fertilization of the egg leading to the formation of the embryo. Pollinators and Pollenizers Pollinator: Agent that moves the pollen Pollenizer: The plant that provides the pollen Cross pollination and Self pollination Some plants are self-fertile or self compatible and can pollinate themselves: other plants have chemical or physical barriers to self pollination and need to be cross-pollinated, therefore pollination can be either through: cross- pollination or self pollination Self incompatibility and precenting self- pollination Recognition factors: That prevents self- fertilization ensures genetic variability. May be similar to an “immune system” in the plant. Recognizes “self” in the proteins displayed on the pollen. This syste, would reject “self” opposite to the animal immune system Self- incompatibility: The ability of a plant to reject its own pollen and the pollen of closely related individuals- soem plants prevent self fertilization by developing stamens and pistils at different times or arrange these reproductive parts in such a way that the animal pollinator cannot accidently transfer pollen within the flower or plant. Development of two types of flowers “pin” and “thrum”. Pin flowers: long and styles and short stamens Thrum flowers: Short styles and long stamens Self pollination and Cross pollination Cross- pollination: Between a pollinator and an external pollenizer. Also called syngamy, pollen is delivered to a flower of a different plant. Self- pollination: Pollen moves to the female part of the same flower or to another flower on the same plant. Also called autogamy. Self pollination is restricted to those plants that accomplish pollination without an external pollinator. For example, stemens actually grow in contact with the pistil plants adapted to self- pollinate have stemens and carpals at the same length. Cleistogamy is autogamy pollination that occurs inside the flower before the flower opens. Flower is called a cleistogamous. Many crop plants are self- pollinating, peas, soybeans, sunflower, tomatoes. To prevent self- fertilization- laborious removal of the anthers or through the development of sterile male plants. Most peach varieties are autogamous- but not truly self- pollinated because the insect transfer pollen to another flower on the same plant. Hybridization: Effective pollination bw flowers of different species (within the same genus) or even bw flowers of different genera (eg orchids). Fertilization process 1.​ Each ovule contains a megasporangiu, tissue which houses the diploid megaspore mother cells that undergo meiosis (2 times) to produce 4 haploid megaspores. -​ In most angiospem species only one megaspore survives  2.​ Later nucleus of this megaspore divides three times without cytokenises to give raise to one large cell with 8 haploid nuclei membranes then form and divide these nuclei up to form the complete female gametophyte or the embryo sac (the female gametophyte is an embryo sac) -​ Within the embryo sac are: ​ Three antopodal nuclei- so called antipodal cells- at one end of the sac, sunction unknown. ​ Two polar nucli- not partitioned but share the cytoplasm of the large central cell of the embro sac ​ 2 synergids- the other end of the sac, flank the egg and function to attract the pollen tube to the egg ​ 1 egg Double fertilization After landing on a stigma- the pollen grains absorbs moisture and begins to germinate (grow). It produces its pollen tube that extends down bw the cells of the style toward the ovary and the ovules. Generative nucleus undergo mitosis and two sperms are developed. They follow tube nucleus which moves forward and extends pollen tube. The tip of the tube enters the ovule through micropyle (a gap) and two sperms are released… then the double fertilization occurs. Double Fertilization (2) -​ One sperm fertilization an egg to produce the zygot which divides to form the embryo -​ Second fertilization involves the union of the second spem with two polar nuclei- forms a triploid nucleus in the center of the ovule. -​ This triploid cell gives rise to the endosperm food storing tissue of the seed After double fertilization, the ovule develops into seed (embryo, endosperm and integuments) Seed and Fruit development The first mitptic division of the zygot is asymmetric. This asymmetry provides the first environmental difference experianced by the differentiating cells and establishes the root- shoot axis. The ovule integumments become the seed coat. Tissues of the ovary (syn. carpal) and sometimes the receptacle become the fruit. There are many kinds of fruits. Fruits aid seed dispersal. The ovary wall becomes wither a dry or fleshy fruit. Many dry fruits are wind dispersed, some dry fruits are animal dispersed, many fleshy fruits are animals dispersed. Some fruits disperse seeds explosivley. Some fruits make seeds buoyant to aid dispersal by water. Asexual reproduction (natural vegetative propagation) This occurs when plants grow and develop naturally without any human interference. Natural vegetative propagation is the growing of new plants from parts of a parent plant such as underground stems, roots and leaves. Bulb: consists of a short stem base with one or more buds enclosed in many fleshy leaves, which store food. Examples: onion, lily, hyacinth and tulip. Corm: Is a thick stem base with scaly leaves at the nodes and contains stordes food. Example: Gladiola and begonia. Tuber: Is enlarged stem part because of stored food. The “eyes” of the potato are its nodes where buds and rootswill develop. Example: potato Rhizome: Is an underground stem that grows horozontlly near the soil surface. Roots and buds develop at the nodes and grow into new plants. Example: ginger Stolons: These stems grow horonzontally above the ground. When the node touches the ground the roots and leaves develop and a new plant grows. Example: strawberry and bermuda. New plants from roots Plants like turnip, carrot, radish and sweet potato (kamote) have storage roots. These roots contain food. When planted, storage roots grow into “new” plants. New plants from the leaves Katakataka has leaves that produce new plant seperate from the parent plant and continue to grop. Begonia plants have also produce new plants form their leaves that touch the soil. Artificial vegetative propagation This is a part of a plant, specifically a stem or leaf is cut and planted in the soil. This method of propagating plants develop by people, who are engaged in the production of plants for food or decoration. Cutting: The cutting produce new roots, stems, or both, and thus becomes a new plant independent of the parent. Layering: Is a teqhniqe for plant propagation in which a portion of an aerial stem is encouraged to grow roots while still attached to the parent plant and then removed and planted as an independent plant. Grafting: a branched or stem is cut from one plant carefully and joined to another. The branch or stem shares the food and water that passes through the stem of the mother plant. Grafting is done to improve the quality of some plants. Its used to speed the maturity of some plants. It provides a strong stalk for some ornamental plants. Repair a damage trunk of a tree which stops the flow of nutrients. Budding: It is done by choosing and cutting a bud from one plant and attaching it to another plant. The bud must fit well to the mother plant. When the bud grows big enough it will become part of the plant. Marcotting (air layering): In marcotting, a healthy mature plant is selected, the bark of the plant stem is removed. Soil must be put around the open stem which is then wrapped with cloth, plastic or coconut husk. In few months time, roots will grow out of the stem. Cloning: Is a method of producing a new plant using tissue of culture. Beginning with a group of cells cut from the part of the mother plant, thousands of exact copies can be produced within a short period. Lecture 3 Anatomical structure of plants (Roots) 1st practical work Functions 1.​ Anchorage and support 2.​ Absorption and conduction 3.​ Storage 4.​ Photosynthesis (mangroves, orchids) 5.​ Aeration (pneumatophores) 6.​ Movement (contractile roots) 7.​ Reproduction Root development Parts of the root: Area of cell division: Short, few mm in long -​ Apical meristerm -​ Root cap (terrestrial plants) Area of elongation: 5-10 mm in long Area of differentintiation (maturation) -​ Up to few cm in long -​ 1mm^2 has 400 root hairs (makes large soak area) Basal zone (all parts above) Growth of a root hair -​ Grows in area of maturation -​ Each root hair is only a part of a single cell Root hair perform a very important functions: -​ Provide plant with water and minerals -​ They exrete acids that aim to make insoluble minerals digestible for plant cells Meristems (growth tissues) Primary meristems: located at the tip of rhe roots Secondary meristems: Develop from primary meristematic cells- procambium and pericycle. Secondary meristems are lateral meristems according to the position and extending along the length of roots and shoots. Secondary meristems characteristics only for dicots. Tip of the root Crossection of the primary root structure Xylem (water conducting tissue) consists of: -​ Tracheids and vessels -​ Sclerenchyma cells (supportive tissue) -​ Parenchyma cells (for collection of nutrients) Pholem (conducting organic materials) consists of: -​ Sieve-tube members (prolonged cells) -​ Companion cells (for nutrient aid) -​ Sclerenchyma -​ Parenchyma cells Dicots and Monocots root structure Dicots plants also have primary root structure but only at a very young parts of roots. Their structure is similar as in monocots but the central part (vascular tissue) differ and xylem like a cross: Periderm (secondry dermal tissue) Cork cambium with cells inside (phelloderm) and outside (phellem) makes periderm- the secondary dermal tissue that replaces the epidermis. Anatomy of some modified roots Roots of some plants for example, radish produce much more xylem than phloem while other plants example, carrots produce more phloem. Anatomy of some modified roots Thick roots of turnips or beetroots have another type of the structure: instead of a single ring of vascular cambium, multiple rings of vascular cambium arrises. This results in fast thickening because each new vascular cambium produces vascular tissue. (secondary xylem and secondary phloem) Lecture 4 Plant anatomy stem practical work 2 Apical meristem and growth Apical meristem: Responsibple for primary growth Leaf primodorium: Developing young leaves Lateral axillary bud: Can develop into branches Primary anatomical structure of stem Young stems arrised from apical meristem have primary structure. Monocot plants have primary structure all their entire life. In dicots plants their stem evolve into secondary structure. Primary structure of a monocotyledon and dicotyledon Lecture 5 Anatony of plants Leaves (3rd practical work) Different types of leaves Internal structure of a leaf Stomata: Opening for gas exchange and transpiration. The epidermal barrier in leaves is interrupted only by stomata, tiny pores flanked by specialized epidermal cells called guard cells. Each stomata is a gap bw a pair of guard cells. The stomata allow gas exchange bw the surrounding air and the photosynthetic cells inside the leaf. They are also the major avenue of evaporative water loss from the plant- a process called transpiration. Crossection of a leaf Lecture 6 Reproductive parts of plants. Fertilization. Fruits (4th practical work) Development of gametes in ovary Development of gametes (pollen grains) in anther