Overview
This lecture covers the organization of plant cells into tissues, explores the three main tissue types in plants (ground, dermal, and vascular), their subtypes, functions, and explains how they enable plant survival and growth.
Levels of Organization in Plants
- Plant cells group into tissues, which then form organs, similar to animals.
- The three main types of plant tissues are ground tissue, dermal tissue, and vascular tissue.
Ground Tissue
- Ground tissue makes up most of a plant's body and is divided into parenchyma, collenchyma, and sclerenchyma.
- Parenchyma tissue handles photosynthesis (mesophyll in leaves), starch storage (roots and seeds), and wound repair.
- Collenchyma and sclerenchyma tissues provide structural support, with thick cell walls made of cellulose or lignin.
Dermal Tissue
- Dermal tissue forms the plant's outer layer (epidermis), typically one cell thick.
- The epidermis protects underlying tissues and secretes a waxy cuticle to prevent water loss and pathogen entry.
- Specialized epidermal cells form hairs for gas/nutrient exchange and herbivore deterrence.
- Stomata (small openings) allow gas and water exchange, regulated by paired guard cells.
- In older plant parts, the epidermis is replaced by the thicker, protective periderm.
Vascular Tissue
- Vascular tissue distinguishes vascular plants from nonvascular plants and allows for nutrient/water transport.
- Xylem (made of dead tracheids and vessel elements) transports water and minerals upward via capillary action and transpiration.
- Phloem (living sieve and companion cells) transports sugars from leaves to the rest of the plant, relying on gravity and water from xylem.
Key Terms & Definitions
- Ground tissue — tissue that makes up most of the plant's body; includes parenchyma, collenchyma, and sclerenchyma.
- Dermal tissue — plant “skin” tissue; protects and prevents water loss.
- Vascular tissue — tissue for transport of water, nutrients, and sugars (includes xylem and phloem).
- Parenchyma — ground tissue for photosynthesis, storage, and repair.
- Collenchyma — ground tissue for flexible support.
- Sclerenchyma — ground tissue for rigid support.
- Epidermis — outermost dermal layer, usually one cell thick.
- Cuticle — waxy layer secreted by epidermis to reduce water loss.
- Stomata — pores in epidermis for gas exchange.
- Guard cells — cells controlling stomata opening/closing.
- Periderm — protective tissue replacing epidermis in older plant parts.
- Xylem — vascular tissue transporting water/minerals up the plant.
- Phloem — vascular tissue transporting sugars throughout the plant.
- Transpiration — water evaporation from leaves, aiding water movement up through xylem.
Action Items / Next Steps
- Review the functions and locations of each tissue type.
- Prepare to learn how tissues organize into plant organs in the next session.