FINALS II BIOLOGY 2 - PLANTS

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  • Gas exchange in plants takes place through stomata.
  • Stomata are the tiny openings present on the epidermis of leaves
  • In some of the plants, stomata are present on stems and other parts of plants. The stomata in plants are enclosed by bean shaped cells called guard cells.
  • Guard cells are cells surrounding each stoma. They help to regulate the rate of transpiration by opening and closing the stomata.
  • Stomata play an important role in gaseous exchange and photosynthesis. The figure below describes the structure of stomata in the epidermis of the leaf.
  • During the day when photosynthesis occurs, the oxygen released from the process is utilized for respiration.
  • A respiratory opening is found under each stoma, and the process of opening and closing of stomata depends on the presence of sugar and starch in the guard cells.
  • Gaseous exchange occurs through diffusion via stomata.
  • Diffusion is the movement of molecules from a region of greater concentration to a region of lesser concentration, in the direction following the concentration gradient.
  • Stomata control the transpiration of water vapor and the exchange of carbon dioxide and oxygen.
  • Stomata are flanked by guard cells that swell or shrink by taking in or losing water through osmosis. When they do, they open or close the stomata.
  • Xylem transports and stores water and water-soluble nutrients in vascular plants. 
  • Phloem is responsible for transporting sugars, proteins, and other organic molecules in plants.
  • XLYEM AND PHLOEM
    A) XYLEM
    B) PHLOEM
    C) XYLEM AND PHLOEM
  • Angiosperm
    • These are flowering plants, the largest and most diverse group within the kingdom Plantae. With around 300,000 species, they represent approximately 80 percent of all the known green plants now living.
  • Gymnosperm
    • Gymnosperms are a smaller, more ancient group, and it consists of plants that produce “naked seeds” (seeds that are not protected by a fruit). There are more than 1,000 species of gymnosperms still found on Earth.
  • Whorl
    • also known as verticil, is an arrangement of sepals, leaves, petals, carpels, or stamens, radiating from a specific point and wrapping around the stalk or stem.
  • The characteristic reproductive structure of angiosperms. As popularly used, the term “flower” especially applies when part or all the reproductive structure is distinctive in color and form.
  • They are called determinate shoots, meaning that they stop growing after the flower and fruit are formed.
  • Vegetative Parts of a Flower
    • The vegetative part of a flower consists of the following
  • Petals: This is a bright-colored part that attracts bees, insects, and birds. The color of petals varies from plant to plant; some are bright while some are pale colored. Thus, petals help us to differentiate one flower from another
  • Sepals: Sepal is the green-colored part beneath the petals to protect rising buds. Some flowers have fused petals-sepals while a few have separated petals-sepals.
  • Reproductive Parts of a Flower
    • Flowers contain the plant’s reproductive structures. A flower includes reproductive parts – the stamen and pistil. A flower may have only female parts, only male parts, or both.
  • Stamen: This is the male reproductive organ and is also known as Androecium. It consists of two parts namely: anther and filaments
  • The anther is a yellowish, sac-like structure, involved in producing and storing the pollens.
  • The filament is a slender, threadlike object, which functions by supporting the anther.
  • Pistil: This is the innermost part and the female reproductive organ of a flower which comprises three parts -stigma, style, and ovary. This is collectively known as the pistil.
  • Stigma: It is the topmost part or receptive tip of carpels in the gynoecium of a flower.
  • Style: It is the long tube-like slender stalk that connects the stigma and the ovary.
  • Ovary: It is the ductless reproductive gland that holds a lot of ovules. It is the part of the plant where the seed formation takes place.
  • Whorls
    Along with the vegetative and reproductive parts, a flower is also composed of four whorls, which are largely responsible for the radial arrangement of a flower.
  • Calyx
    • The calyx is the outermost whorl of a flower. It comprises sepals, and tiny leaves present at the base of a flower. These protect the flower whorls against mechanical injuries and desiccation.
  • Corolla This is the second whorl of a flower. It contains petals which serve two main functions:
    • To attract pollinators.
    • To protect the reproductive parts of a flower
  • Stamens or Androecium
    • Stamen is also known as the third whorl of the flower and is the male reproductive part.
  • Stamens or Androecium
    • It consists of a filament which is a thread-like structure with a circular structure anther on the top.
  • Pollen is produced by the anther which contributes to the male reproductive process of the plant. All the stamens do not bear fertile anthers.
  • Carpels or Gynoecium
    • The carpels contain the pistil, the female reproductive part of the flower. It comprises the ovary, style, and stigma. The egg or the ovule is present in the ovary.
  • Complete Flower
    • A complete flower is one that consists of sepals, petals, stamens and pistils. On the contrary, an incomplete flower is one that lacks one or more of these structures.
  • Incomplete Flower
    • defined as a flower missing any of its parts in its natural form, i. e. petals, sepals, stamens or pistils
  • Perfect/Bisexual
    • The flower possessing both male and female reproductive parts are a bisexual flower that is both stamens and carpels are present in the same flower.