An overwiev of a flowering plant Main root
Root Roots of most plants are covered with root hairs. Their function is to increase root surface area for more efficient absorption of water and nutrients from the soil. Every root hair is a single cell.
There are many root types. The most common two types are tap roots (straight roots) and fibrous roots. Some tap roots can be specialized for storage of water and nutrients (carrot, beet, raddish etc.).
Exotic root functions Besides mechanical support or better supply of oxygen, aerial roots can be specialized to absorb moisture from humid air (orchids).
Stem Main functions of plant stems: 1. Mechanical support of leaves and flowers. 2. Transport of water and nutrients. There are also several specialized stem types. Rhizomes, bulbs and tubers look like roots, but in reality they are stems with storage functions. Stolons are stems that help plants such as strawberry spread around.
Leaf Main functions of plant leaves: 1. Photosynthesis. 2. Evaporation of water (transpiration) as a motive force for water movement in root and stem. Depending on plant environment (dry or wet, much light or little light, cold or hot etc.), there can be many different types of leaves.
Leaves can be specialized for climbing/meachanical support (garden pea) protection from animals (cactus) storage (succulents) vegetative/asexual reproduction (Kalanchoe) attraction of pollinators (Puansettia, Bugenvillia) catching and digesting small animals (carnivorous plants)
Plants are composed of three main tissue types: Dermal tissue (protection, absorption) Ground tissue (photosynthesis, storage) Vascular tissue (transport of water, nutrients and signals)
Extracellular components of a plant cell - Primary cell wall (cellulose) - Middle lamella (pectin) - Secondary cell wall - (cellulose + proteins + lignin)
Example of ground tissue: parenchyma Parenchyma cells perform most of the metabolic functions in the plant: synthesis and storage. Relatively thin and flexible primary cell wall. No secondary cell wall. The ability to divide and differentiate into othe cell types under particular conditiones, for example, during wounding and in tissue culture (in vitro culture).
Example of ground tissue: collenchyma Collenchyma cells provide mechanical support for young growing tissues. It is a «flexible» support without restraining the growth. Primary cell walls are thicker then in parenchyma cells. No secondary cell wall.
Example of ground tissue: sclerenchyma Sclerenchyma cells provide very rigid mechanical support. Secondary cell walls are very thick and contain large amount of lignin. Lignin constitutes 25% of wood dry mass. Sclereid cells make nut shells so strong. Hemp fiber cells are used for making ropes. Linen tissue is made of flax fiber cells.
Water-conducting cells of the xylem Xylem tissue provides both mechanical support and route for water transport. Secondary cell walls are very thick and contain large amount of lignin. Vessel elements and tracheids are long cells that are dead at functional maturity. Interior of these empty cells is used as a water pipe inside the plant.
Sugar-conducting cells of the phloem Phloem tissue provides route for sugar transport. Sieve-tube elements (phloem cells) are alive at functional maturity. These cells lack nucleus, vacuole, ribosomes and cytosceletal elements to make movement of solutes across the cell easier. Sieve-tube elements are kept alive by metabolic activity of closely attached cells (companion cells). Companion cells also help in loading and unloading of sievetubes with sugars.
Small insects, e. g. aphids, mosquitos, have a special system for sucking phloem sap (solution), which is reach in sugars. Aphids excrete excess of sugars, which is collected by ants. Ants protect aphids and use them as their «domestic» animals, or «cows».
Phloem sap (solution, juice) from birch tree is being collected commercially in Russia, Ukraine and Belarus. An adult birch tree gives 2-3 litre of juice per day. The juice has very pleasant sweet taste and contains beneficial compounds such as vitamins B6 and B12.
Cells/tissues that produce energy-rich products of photosynthesis (sucrose) are called source cells/tissues (source of energy). Places where the energy-rich substances are consumed or deposited are referred to as sink cells/tissues (the energy is «sunk», it disappears, hence the name «sink»). source sink
Plants grow all the time through their lives, because they have perpetually undifferentiated tissues called meristems. Meristems give rise to all other cell types (similar to the embryonic stem cells in animals).
Meristem types Apical meristem (shoot AM and root AM) Lateral meristem, or cambium (vascular cambium and cork cambium) Intercalary meristem (only in grasses and some other plants).
Internal design of the root is different between two-cotyledon plants (dicots) and one-cotyledon plants (monocots, most grasses)
Water and mineral nutrients can be transported to the root center (xylem) via different pathways: 1. Through apoplast (cell walls) - uncontrolled movement inside of cell walls. 2. Through symplast (cytoplasm and plasmodesmata) - movement controlled by plasmodesmal elements.
Water and mineral nutrients can be transported to the root center (xylem) via different pathways: 3. Through plasma membrane (transport proteins) - movement controlled by transporters located in plasma membrane.
Endodermis one-cell layer inside the root every endodermis cell is surrounded by a «belt» (Casparian stip) made of very hydrophobic material called suberin these «belts» block apoplastic transport of nutrients from outside to inside of the root this way plant has possibility to control what nutrients to import into root xylem for transport to other parts of the body xylem xylem
Internal design of the shoot is different between two-cotyledon plants (dicots) and one-cotyledon plants (monocots)
Example of stem growth in a woody plant Every year vascular cambium produces new xylem and phloem; cork cambium produces new cork to better protect the stem.
Example of stem growth in a woody plant Growth rings are formed by secondary xylem. The number of growth rings indicates the age of a tree.
Dendrochronology The width of growth rings can give information about climate during certain year. Warmer years correspond to wider growth rings.
Xylem grows much faster than phloem
Details of leaf anatomy
Flowers originate from ancestral organs similar to cones of pine tree. All parts of a flower derive from leaves specialized for sexual reproduction.
Development of pollen grains (male) and embryo sac (female)
Pollen grains are variable in shapes, each specialized for transfer by wind, animals or water. Pollen grains are responsible for allergic reactions in humans.
Growth of a germinated pollen tube
Double fertilization
Plant embryo development
Dicot seed germination Monocot seed germination Onion
Bristlecone pine - the oldest living organism on the Earth (5064 years old, White Mountains, California) Thank you for your attention!