Plants Conclusion

Objectives

• Outline the function and growth of stems
• Describe the structure and function of leaves
• Describe a general plant life cycle

Roots and stems are made of dermal, vascular, and ground tissue.

In trees some epidermal tissue is replaced by bark. The inner part of bark is alive and growing; the outer part of bark is dead and provides protection.

Ground tissue forms the interior of the stem. Large central vacuoles of ground tissue cells fill with water to support the plant. The vacuoles may also store food.

Bundles of vascular tissue run through the stem and transport fluid.

Leaves

The primary role of leaves is to collect sunlight for photosynthesis.

Non-Flowering Plants: Types of Leaves

• Microphyills
• Fronds
• Needles

Flowering Plant Leaf Parts

• Blade - wide, flat part
• Petiole - part that attaches to the stem

The form and arrangement of leaves maximizes light exposure while conserving water.

Shorter days and cooler weather signal leaves to produce less chlorophyll.

Plants shed these leaves to reduce water loss. Plants that shed leaves each year are deciduous.

Deciduous trees must use a lot of energy each year to regrow leaves.

Evergreen plants do not have to grow new leaves and have needles to minimize water loss.

However, needles have a small surface area with which to collect light, so they have a greater concentration of chlorophyll.

Leaf Tissues

• Mesophyll - where photosynthesis occurs
• Veins - made of xylem and phloem
• Epidermis - single layer that secretes waxy cuticle

Plant Life Cycle

Alteration of Generations

• Diploid sporophyte and haploid gametophyte
• Sexual and asexual

Diploid sporphyte undergoes meiosis to form haploid spores.

A spore develop into a haploid gametophyte, which has male or female reproductive organs that undergo mitosis to form haploid gametes.

Fertilization of gametes results in a diploid zygote. The zygote grows and develops into a mature sporophyte to repeat the cycle.

One of the two generations usually is dominant.

Dominant Generation

• Nonvascular plants: gametophyte
• Vascular plants: sporophyte