Lecture 8 - Introduction to Plant Life

What is a plant?

• Multicellular eukaryote that produces its own food through photosynthesis.

  •  Mostly terrestrial (land dwelling).

  • Sessile (stay in one place).

  •  Range from 1 millimeter to 380ft tall!

Evolutionary History of Plants 

• Diagram showing evolutionary relationships among organisms 

  • What is more related to what? 

• Groups organized by their shared traits.

  • Common ancestry 

Nonvascular Seedless Plants

• Mosses, Liverworts, Hornworts.

• Lack vascular tissue 

  • Limited vertical growth 

• Rhizoids 

  • Not true roots 

• Spores: asexual reproduction 

• Flagellated sperm 

  • Wet environments

Vascular Seedless Plants 

• Ferns, Clubmosses & Horsetails 

• Vascular Tissue 

  • Secondary growth 

• True Roots 

• Spores: asexual reproduction 

• Flagellated sperm 

  • Wet environments 

Vascular Tissue: 

• Tube life vessels that transport water & nutrients 

  • Xylem: moves water up a plant 

  • Phloem: Moves food up or down a plant 

Vascular Bundles:

• bundles of xylem & phloem within the roots, stems, and leaves of the plant.

Plant Morphology 

• Shoot System

• Stem

• Leaves

• Buds

• Root System

Shoot System:

• photosynthesis & reproduction 

• Stem:

• produce leaves, branches, and flowers, transports nutrients and water from roots to leaves

Leaves

• primary location of photo synthesis

Buds

• undeveloped shoot

Root System:

• anchors plant, absorbs minerals & water, and stores carbohydrates

Roots 

• Taproot or fibrous root 

• Absorb water, minerals, nutrients 

• Root hairs 

  • Increases surface area 

Mycorrhizae: 

• Symbiotic relationship between a fungus and plant roots 

  • Fungus receives sugars 

  • Plant receives more water & nutrients 

Vascular Seed Plants 

• Gymnosperms

• Angiosperms

Gymnosperms

• seed bearing vascular plants in which the seed is enclosed in an ovary 

  • Naked seed

  • Cone bearing

Angiosperms

• seed bearing vascular plant in which the seed is enclosed in an ovary 

  • “Enclosed seed” 

  • Flowering plants: fruits 

Seed = protection and food supply 

• Protective layer (seed coat) 

  • Longer life span 

Cotyledon

seed leaves

Endosperm

energy rich tissue that nourishes developing embryo

Gymnosperms

• Conifers, Ginkgos, and Cycads 

• Approximately 1000 species 

  • Most 680 are conifers 

• Major ecological importance 

Gymnosperm Dispersal 

• Wind dispersal of pollen and seeds

Angiosperms

• 300,000 species of flowering plants 

  • Food crops (fruits, corn, vegetables, wheat) 

  • Mostly trees, but a diverse array of life forms 

    • Grasses 

    • Forbs (wildflowers) 

    • Succulents 

Flower Anatomy 

• Sepal: protects developing flower 

• Petals: attract pollinators 

• Carpel: female reproductive parts 

  • Stigma 

  • Style 

  • Ovary 

• Stamen: male reproductive parts 

  • Filament:stalk 

  • Anther: pollen production

Pollination in Angiosperms 

• Each pollen grain contains two sperms cells & one tube cell 

  • Tube cell forms pollen tube 

• Pollination: the transfer of pollen from the male anther to the female stigma 

• Double Fertilization: One sperm cell fuses with egg forming the zygote, while the other sperm cell fuses with nuclei within the ovule to form endosperm

Angiosperm Life Cycle 

1. Microspores in anther develop into pollen grains, with one tube cell and two sperm cells.

2. Megaspore in the ovary develops into an embryo sac with egg.

3. Pollen grain contacts stigma (pollination) and pollen tube forms.

4. One sperm fertilizes egg forming zygote, one sperm fertilizes nuclei forming endosperm.

5. Embryo and endosperm develop into a seed.

6. Seed grows into a mature plant.

• Simple Fruit: 

• develops from a single ovary 

• Aggregate Fruit: 

• Develops from several ovaries (carpels) in the same flower. 

• Multiple Fruit: 

• Develops from ovaries (carpels) of multiple flowers 

Transpiration:

• Loss of water from above ground plants parts by diffusion and/or evaporation 

Cohesion-tension hypothesis 

• Transpiration provides the force that pulls water molecules bound by cohesion, from the roots to the leaves 

Trade-off between Leaf Size and Transpiration 

• Larger leaf size = more light capture, but more water loss 

  • Tropical environments 

• Small leaf size = less light capture, but less water loss 

  • Dry, exposed environments 

    • Deserts 

    • Temperature forests 

Adaptations to Reduce Transpiration 

• Small, thick leaves 

  • Reduce water loss 

• Thick cuticle 

• sheltered/hairy stomata 

• Lose their leaves 

  • Drought deciduous 

• C4 & CAM plants: 

  • Grasses, cacti 

Nutrient Transport in Plants 

• sugar- rich xylem sap rises up the trunk in late winter to fuel lead and flower production 

  •  “Real” maple syrup 

Apical Meristem 

• Group of cells located in the root and shoot tips that give rise to all plant issues. 

  • Regions of cell growth and differentiation 

Vascular Bundle 

• Gives rise to secondary xylem & phloem 

  • Secondary xylem = tree rings 

Human use of Seed Plants 

• Wheat, corn, and rice provide nearly 60% of plant calories consumed 

  • Potatoes, cassava, sweet potatoes also top crops 

• Medications 

  • 25% of medications come from plants 

  • Oxygen 

  • Wood 

  • Paper 

Deforestation:

• 14 million acres of tropical rain forest cleared every year 

Causes: 

• Private farming 

• Commercial agriculture 

• Logging 

• Collective wood for fuel