Plant Structure, Growth, Nutrition, and Animal Diversity: Key Concepts and Features

Study Guide - Smart Notes

Tailored notes based on your materials, expanded with key definitions, examples, and context.

Plant Structure and Growth

Dermal Tissue in Plants

The dermal tissue system forms the outer protective covering of plants. It serves as the first line of defense against physical damage and pathogens.

Location: Dermal tissue is found on the outermost layer of all plant organs, including roots, stems, and leaves. In non-woody plants, it is primarily composed of a single layer of cells called the epidermis.
Function: Protects against water loss, regulates gas exchange, and may have specialized structures such as root hairs and trichomes.
Example: The waxy cuticle on leaves is produced by epidermal cells and reduces water loss.

Sieve-Tube Elements and Phloem Function

Sieve-tube elements are specialized cells in the phloem responsible for transporting sugars and other organic nutrients throughout the plant.

Structure: Sieve-tube elements are elongated, living cells joined end-to-end to form sieve tubes. Their end walls, called sieve plates, have pores to facilitate flow between cells.
Function: Transport of sugars (mainly sucrose) from photosynthetic tissues (sources) to non-photosynthetic tissues (sinks) such as roots, fruits, and growing shoots.
Example: During the growing season, leaves act as sources and roots as sinks for sugar transport.

Primary Plant Growth

Primary growth increases the length of roots and shoots, allowing plants to extend and explore new areas for resources.

Location: Occurs at apical meristems found at the tips of roots and shoots.
Process: Cells divide and elongate, resulting in vertical growth.
Example: The elongation of a seedling's root as it pushes through soil.

Secondary Plant Growth and the Vascular Cambium

Secondary growth increases the thickness (girth) of stems and roots, primarily in woody plants.

Vascular Cambium: A lateral meristem that produces secondary xylem (wood) to the inside and secondary phloem to the outside.
Function: Enables plants to grow wider and support larger structures.
Example: Formation of annual growth rings in trees.

Role of Ovaries in Plant Flowers

The ovary is a key reproductive structure in flowers.

Function: Protects ovules (future seeds) and, after fertilization, develops into a fruit.
Importance: Fruits aid in seed dispersal by attracting animals or using other mechanisms.
Example: An apple develops from the ovary of a flower and contains seeds.

Plant Nutrition and Transport

Physical Forces in Xylem and Phloem Transport

Plants use different mechanisms to move water, minerals, and sugars through their vascular tissues: xylem and phloem.

Xylem Transport: Driven by transpiration (evaporation of water from leaves), cohesion (water molecules stick together), and adhesion (water molecules stick to cell walls).
Phloem Transport: Driven by a pressure gradient created as water follows sugars loaded into sieve tubes at source tissues and is pulled by sugar sink cells at sink tissues.
Example: Water moves upward from roots to leaves in xylem; sugars move from leaves to roots in phloem.

Water Absorption and the Casparian Strip

Roots absorb water and minerals from the soil, but entry into the vascular system is regulated by the Casparian strip.

Casparian Strip: A band of suberin (waxy substance) in the cell walls of endodermal cells that blocks passive flow of substances into the stele (vascular cylinder).
Function: Forces water and dissolved minerals to cross cell membranes, allowing selective uptake and exclusion of harmful substances.
Example: Prevents toxins in soil from entering the plant's vascular system.

Macronutrients Absorbed by Plants

Plants require several macronutrients for growth and metabolism.

Carbon: Absorbed as CO2 from the air.
Oxygen, Hydrogen, Nitrogen: Absorbed from the soil (O and H mainly as water; N as nitrate or ammonium).
Other Macronutrients: Potassium (K), Phosphorus (P), Calcium (Ca), Magnesium (Mg), and Sulfur (S).
Example: Nitrogen is essential for amino acids and nucleic acids.

Role of Mycorrhizae in Plant Nutrition

Mycorrhizae are symbiotic associations between plant roots and fungi.

Function: Fungi increase the surface area for water and mineral absorption, especially phosphorus.
Benefit: Plants provide fungi with carbohydrates produced by photosynthesis.
Example: Most terrestrial plants form mycorrhizal associations.

Role of Bacteria and Fungi in Fertilizing Topsoil

Soil fertility depends on the activity of bacteria and fungi.

Bacteria: Decompose organic matter, fix atmospheric nitrogen, and convert it into forms usable by plants.
Fungi: Decompose complex organic materials, releasing nutrients into the soil.
Example: Rhizobium bacteria in legume root nodules fix nitrogen.

Animal Diversity: Invertebrates and Vertebrates

Characteristics of Flatworms

Flatworms (phylum Platyhelminthes) are simple, bilaterally symmetrical invertebrates.

Body Plan: Flattened, unsegmented bodies with no coelom (body cavity).
Digestive System: Incomplete; a single opening serves as both mouth and anus.
Other Features: Many are parasitic; free-living forms include planarians.
Example: Tapeworms and flukes are parasitic flatworms.

Characteristics of Arthropods

Arthropods are the most diverse animal phylum, including insects, arachnids, crustaceans, and myriapods.

Body Plan: Segmented bodies, jointed appendages, and an exoskeleton made of chitin.
Growth: Must molt (shed exoskeleton) to grow.
Example: Insects (beetles, butterflies), spiders, crabs.

Distinctive Features of Chordates

Chordates (phylum Chordata) share four key features at some stage of development.

Notochord: Flexible, supportive rod along the back.
Dorsal Hollow Nerve Cord: Develops into the brain and spinal cord.
Pharyngeal Slits: Openings in the throat region.
Post-Anal Tail: Tail extending beyond the anus.
Example: All vertebrates (fish, amphibians, reptiles, birds, mammals) are chordates.

Relative Abundance of Invertebrates and Arthropods

Invertebrates make up the vast majority of animal species, with arthropods being the most numerous group.

Invertebrates: Animals without a backbone; over 95% of all animal species.
Arthropods: Account for more than 80% of described animal species.
Example: Beetles alone represent the largest group of arthropods.

Vertebrate Diversity

Defining Characteristics of Vertebrates

Vertebrates are chordates with a backbone or vertebral column.

Features: Endoskeleton of bone or cartilage, skull, and complex organ systems.
Example: Fish, amphibians, reptiles, birds, and mammals.

Ectothermic Animals

Ectotherms are animals that rely on external sources to regulate their body temperature.

Examples: Reptiles (snakes, lizards), amphibians, most fish.
Contrast: Endotherms (birds, mammals) generate heat metabolically.

Distinguishing Traits of Mammals

Mammals are vertebrates with unique features.

Hair: Provides insulation and sensory functions.
Mammary Glands: Produce milk to nourish young.
Other Features: Three middle ear bones, differentiated teeth.
Example: Humans, whales, bats.

Characteristics of Most Fish

Most fish possess specialized structures for respiration and buoyancy.

Operculum: A bony flap covering and protecting the gills.
Swim Bladder: An internal gas-filled organ that helps maintain buoyancy.
Example: Bony fish such as salmon and trout.

Distinguishing Features of Sharks and Rays

Sharks and rays are cartilaginous fish (class Chondrichthyes).

Skeleton: Composed of cartilage rather than bone.
Other Features: Lack swim bladders; have multiple gill slits.
Example: Great white shark, manta ray.

Characteristics of Tetrapods

Tetrapods are vertebrates with four limbs.

Adaptations: Limbs with digits, lungs for breathing air, and adaptations for life on land.
Groups: Amphibians, reptiles, birds, and mammals.
Example: Frogs, lizards, humans.