Lesson 2: Plant Structure and Function

Lesson 2: Plant Structure and Function

• This lesson is part of Module 19: Introduction to Plants (pages 513 to 522).
• All multicellular organisms, including plants, have cells and tissues that work together to maintain homeostasis.
• Plant cells and animal cells have differences and similarities.
• Plant cells and tissues help plants maintain structure and homeostasis.
• The focus question is: What are the structures and functions of plant cells and tissues?
• Plant cells are characterized by cell walls, large central vacuoles, and chloroplasts.
• A vacuole is a structure inside a cell that contains cell sap (fluid), surrounded by a membrane called the tonoplast. The large central vacuole in a plant cell is a key example.
• Plants have many types of cells adapted to specific functions.
• Parenchyma cells are involved in storage, photosynthesis, gas exchange, protection, and tissue repair and replacement (e.g., potato cells).
• Collenchyma cells provide support and transport materials.
• Sclerenchyma cells support surrounding tissues, provide flexibility, and are involved in repair.
• A tissue is a group of cells that work together to perform a function. Plants have four main types of tissues: Meristematic, Dermal, Vascular, and Ground.
• The apical meristem produces cells that increase the length of a stem.
• As plants grow taller, increasing stem diameter provides additional support.
• The age of a tree can be estimated by counting the annual growth rings.
• Root hairs increase the root's surface area, enabling roots to absorb more water and materials.
• The cuticle is made of fatty substance that reduces water loss and prevents bacteria from entering the plant.
• Stomata are small openings on the epidermis through which gases pass; guard cells regulate the opening and closing of stomata.
• Trichomes are hair-like projections that protect the plant from insects and animal predators. The tiny glands on the tips of trichomes may contain toxic substances.
• Vascular tissue (Xylem and Phloem) transports water, food, and dissolved materials throughout the plant.
  • Xylem is the water-carrying tissue in vascular plants, made of vessel elements and tracheids. Vessel elements are tubular cells stacked end-to-end; tracheids have pitted ends and are less efficient at transporting water.
  • Phloem is the main food-carrying tissue in vascular plants, composed of sieve tube members and companion cells. Sieve tube members lack nuclei and ribosomes when mature, but are supported by companion cells.
• Ground tissue consists of parenchyma, collenchyma, and sclerenchyma cells, and is responsible for photosynthesis, storage, and support.
• Roots:
  • The root cap protects root tissues as the root grows.
  • The cortex is composed of ground tissue that transports and stores substances
  • The endodermis is the inner boundary of the cortex and forces water and substances to pass through the endodermal cells, rather than around them.
  • The pericycle produces lateral roots.
• Types of roots include: taproot (e.g., carrots), fibrous (e.g., grass), modified (e.g., storage roots like beets, and other specialized forms like pneumatophores or prop roots).
• Stems:
  • The main function of stems is to support leaves and reproductive structures.
  • Herbaceous stems are soft, flexible, and capable of photosynthesis.
  • Woody stems are rigid and fibrous.
• Leaves:
  • The main function of leaves is photosynthesis.
  • Leaves have a blade and a petiole (stalk).
  • The blade has an upper and lower epidermis, mesophyll (palisade and spongy), and vascular bundles. The spaces in the spongy mesophyll allow gases to move between them to facilitate photosynthesis.
  • Water evaporates from leaves through stomata in a process called transpiration, which can help pull water up from roots.
• Types of leaf arrangement include opposite (leaves across from each other), alternate (leaves staggered along stem), and whorled (leaves arranged in a ring).
• Plant responses:
  • Nastic responses are plant responses to stimuli that aren't dependent on the direction of the stimulus and are reversible.
  • Tropisms are plant growth responses to external stimuli (positive if growth is toward; negative if growth is away from the stimulus). This includes phototropism (light), gravitropism (gravity), and thigmotropism (mechanical touch/support).

Quiz (examples of questions and answers about plant anatomy)

• Question 1: Which plant structure is NOT part of a root?
  • Answer: Stomata (stomata are on leaves)
• Question 2: Which controls the movement of water vapor through stomata?
  • Answer: Guard cells
• Question 3: Which vascular tissue transports water and dissolved minerals from roots to leaves?
  • Answer: Xylem
• Question 4: Which fill(s) the space between spongy mesophyll cells?
  • Answer: Gases
• Question 5: Which describes a positive phototropism?
  • Answer: The plant grows toward the light.