Plant Structure

Angiosperms Flower Structure

  • All have same characteristics:

  • Flowers - specialized shoot used for sexual reproduction.

Contains sepals (protection until blossoming), petals (attraction to pollinators), stamen (male part), carpel (female part)

Structure of Angiosperms

  • Carpel (1 or more is a pistil):

    • Stigma - sticky area where pollen is received

    • Style - leads from stigma to ovary

Ovary - where ovule(s) contained

Stamen:

  • The stalk is the filament (allows stamen to be higher up in the flower)

  • Anther - where pollen is produced.

  • Fruit develops when a seed (fertilized ovule) is created.

  • The fruit is the fleshy part (or in some cases a dry part - like a nut) that protects the developing embryo while aiding in their dispersal.

  • Some flowers can self-pollinate, but most have ways to ensure cross-pollination.

  • Double fertilization: 2 sperm are discharged.

    • 1 fertilizes the egg (embryo)

1 fertilizes the large central cell (has 2 nuclei) - becomes the triploid endosperm (nutrition for the growing embryo)

  • After fertilization, the ovule matures into a seed.

  • Zygote develops into sporophyte with one or two cotyledons (first leaves - monocots have one; dicots have two)

Most angiosperms are dicots (aka eudicots)

  • Angiosperms have a close relationship with their pollinators. 

  • Coevolution has allowed specificity between pollinator and flower to ensure the successful transfer of pollen from one member of a species to another member of the same species.

  • Plants contain natural chemicals that humans have extracted for their own medicinal purposes.

  • For example, menthol is a throat soother that is derived from the eucalyptus tree.

Plant Structure, Growth, and Development

  • Root system (underground)

  • Roots anchor vascular plants in the soil

    • Taproot - one large root; gives rise to lateral roots

    • Fibrous roots - act like a mat

Root hairs increase surface area

  • Stems separate leaves allowing them to get sun.

    • Made of nodes (leaves attached) and internodes (section between nodes)

    • Axillary buds → branches.

    • Apical buds →  growth upwards

  • Leaves - photosynthetic part of the plant.

Blade (flat part) and Petiole (stalk)

  • Dermal tissue - protects the plant.

    • Epidermis (nonwoody plants) - top layer.

    • Also composed from cuticle.

Periderm (woody plants) - replaces epidermis as it ages.

  • Vascular tissue (stele, collectively)- conducts water and nutrients throughout the plants

    • Xylem - conducts water

    • Phloem - conducts sugar

  • Ground tissue does not fall in either category.

    • Internal to vascular tissue - pith

    • External to vascular tissue - cortex.

Meristems are responsible for growth (indeterminate growth)

  • Apical meristems - tips and shoots; aids in growth in length (primary growth)

Lateral meristems - growth in thickness (secondary growth)

Root Growth:

  • Ground tissue fills cortex.

  • Endodermis (innermost layer) is a barrier that protects it.

  • Root pushes through epidermis.

Shoot Growth:

  • Leaf primordia on sides of apical meristems allow for leaf growth.

  • Axillary meristems' buds provide for branching.

Leaf organization:

  • Pores (stomata) allow for gas exchange in leaves.

The opening and closing is controlled by guard cells that regulate gas flow by moving water to open and close the stomata.

Secondary Growth:

  • Increases diameter of stems and roots.

    • Adds secondary xylem to interior (wood), secondary phloem (inner bark) to exterior.

    • In winter, vascular cambium becomes inactive, which results in growth rings.