Chapter 31

Angiosperm Structure and Function

Kingdom Plantae: eukaryotic, multicellular, photosynthetic organisms. All have cell wall, roots, stems, leaves, and gametangia to produce gametes, reproduce sexually. Some of the oldest organisms on earth. Ex: redwood over 100 feet, and giant sequoia or general Sherman is 84 meters tall and 10 m in diameter, 1700 years old.

Plants are divided into 2 major groups:

  • Gymnosperms: non flowering plants, naked seeds that are not in a fruit. Ex: pine, spruce
  • Angiosperms: flowering plants, covered seeds, live everywhere. Many of our food comes from these plants: roots ( carrots, beets), fruits ( apples, nuts), grains ( rice, corn).There are 2 types of angiosperms:
  1. Monocotyledons: one seed leaf; have leaves with parallel veins, complex arrangement of vascular tissue, petals and flower parts are in multiples of 3's, roots are fibrous. Ex: orchids, lilies, grasses, rice, wheat.
  2. Dicotyledons: embryo has 2 seeds; most trees and shrubs, food crops. leaves are multibranched, vascular tissues are arranged in a ring, flowers and petals are multiples of 4 or 5, and roots are taproots that bury deep in the ground. Ex: maple, cactus, rose families, pears, peaches...

PLANT BODY: Roots and shoots that are important in getting water, photosynthesis, release of CO2 and O2.

  1. ROOTS: below the ground, has root hairs.
  2. anchors plant
  3. absorbs and transports water and minerals
  4. stores food
  5. root hairs absorb water and increase surface area.
  6. modified rots like carrots, turnips, beets are large taproots

2. SHOOTS: above the ground, stems, leaves, flowers ( reproductive structures)

  • Stems support leaves and flowers: trunk, branches. Have nodes where leaves attach, and internodes between nodes.
  • Modified stems; runners: grow along surface like strawberries; rhizomes: brownish grow just below soil to store food; tubers: large structures at the end of rhizomes for food storage.
  • Leaves main site for photosynthesis. A leaf has a blade and petiole
  • Buds are growth sites; terminal bud at the tip of a stem, increases length. Axillary bud on the angles of leaves are dormant. Apical dominance occurs when the terminal bud inhibits the growth of axillary buds.

PLANT CELL:

  • Have chloroplasts with chlorophyll
  • large central vacuole for firmness
  • have a cell wall made of cellulose ( carbohydrate)
  • have plasmodesmata which are channels of communication between plant cells
  • Parenchyma cells:
  • most abundant type of cell
  • remain alive when mature
  • have a thin primary wall
  • food storage, photosynthesis, aerobic respiration
  • can become other types of cells after cell injury
  • Collenchyma cells:
  • very thick primary cell wall
  • provide support in growing parts of a plant
  • elongate with growing stem

3. Sclerenchyma cells:

  • rigid secondary walls ( lignin)
  • found in non growing regions
  • support the plant
  • dead when they mature
  • two types fiber long and slender ( rope); sclereid shorter, thick and irregular wall ( nutshells)

PLANT TISSUES: Vascular plants have tissues to move water and food up and down the plant body. There are 3 tissue systems in plants.

  1. Epidermis: skin
  2. covers and protects plant
  3. 1st line of defense against physical and infectious agents
  4. cuticle a waxy layer that protects plants from drying
  5. leaves have pores called stomata for gas exchange, guard cells that regulate size of stomata.

2. Vascular tissue:

a. xylem is the water conducting cells upward from roots

b. phloem is sieve tubes that conduct food and sugars from leaves to other areas

3. Ground tissue:

a. bulk of a young plant

b. fills between epidermis and endodermis

c. mainly parenchyma

d. mesophyll is ground tissue of a leaf, for photosynthesis

PLANT GROWTH: plants exhibit indeterminate growth, which indicates that plants continue to grow as long as they live. Does not mean they are immortal.

Plants are:

  • Annuals: complete life cycle in one year. Ex: wheat, corn, rice
  • Biennials: complete cycle in 2 years. ( carrots, beets)
  • Perennials: plants that live for many years ( trees, shrubs, grasses)

Growth in plants is possible because of tissues called meristems. These are localized, unspecialized cells that divide and generate new cells and tissues.

Primary growth: is growth in length ( root or shoot)

Secondary growth: increase in girth

Primary growth:

  • Apical meristems: grow at the tip of roots and in terminal areas.
  • Root cap is a cone of cells that protect the cells of the root's meristem.
  • These cells are involved in replacing cells that are scraped off and in producing cells for primary growth downward of a root.
  • Cells divide and then elongate to increase in length.
  • Cells of the vascular tissue differentiate into primary xylem and primary phloem.

Secondary growth:

  • increases width and girth
  • more seen in woody plants where the stems form thick layers of dead xylem called wood.
  • vascular cambium layer of actively dividing cells between xylem and phloem
  • vascular cambium gives rise to secondary xylem and secondary phloem
  • secondary growth adds cells to each side of the vascular cambium.
  • secondary xylem is inside the vascular cambium, a new layer is produced every year ( seen as rings that can estimate age of plant). makes up the wood of plants, causes most of the growth in girth
  • secondary phloem outside the vascular cambium, part of the bark and does not accumulate during the years. It is sloughed off.
  • Cork cambium is the layer outside the phloem, is part of the bark and gives rise to cork. cork is an outer layer of plant where the cells are dead with thick walls to protect the underlying stem.

TRUNK:

  • Wood rays are parenchyma cells that transport water to the outer living tissues.
  • Heartwood is center of trunk, older layers of secondary xylem. Dead cells filled with resin.
  • Sapwood is younger secondary xylem that moves water.
  • Bark is secondary phloem, cork cambium, cork.