General Biology: Plant Structure, Nutrition, and Animal Diversity

Chapter 31: Plant Structure, Growth, and Reproduction

Plant Dermal Tissue

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 called the epidermis; in woody plants, it is replaced by periderm (bark).

• Function: Protects against water loss, regulates gas exchange, and may have specialized structures like root hairs or trichomes.

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: Elongated, living cells joined end-to-end, forming sieve tubes. They lack nuclei at maturity and are supported by companion cells.

• Function: Transport sugars (mainly sucrose) from sources (like leaves) to sinks (such as roots, fruits, or growing tissues).

• Example: Movement of sugars from photosynthetic leaves to developing fruits.

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.

• Result: Elongation of plant organs, formation of primary tissues (dermal, ground, and vascular tissue).

Secondary Plant Growth and Vascular Cambium

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

• Vascular Cambium: A lateral meristem that produces secondary xylem (wood) to the inside and secondary phloem to the outside.

• Result: Formation of annual rings in trees, increased support and transport capacity.

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 fruit.

• Importance: Fruits aid in seed dispersal by attracting animals or using other mechanisms.

Chapter 32: 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: Water moves upward from roots to leaves by transpiration (evaporation from leaves), cohesion (water molecules stick together), and adhesion (water sticks to xylem walls).

• Phloem: Sugars move from sources to sinks via a pressure gradient. Water follows sugars into phloem by osmosis, creating pressure that pushes sap toward sink cells.

Water Absorption and the Casparian Strip

Roots absorb water and minerals from the soil, but entry into the vascular cylinder is regulated.

• Casparian Strip: A waxy barrier in the endodermal cell walls that forces water and solutes to cross cell membranes, ensuring selective uptake into the xylem.

Macronutrients Absorbed by Plants

Plants require several essential elements for growth, called macronutrients.

• Carbon (C): Absorbed as CO2 from the air; forms the backbone of organic molecules.

• Oxygen (O), Hydrogen (H): Obtained from water and air; essential for cellular processes.

• Nitrogen (N): Absorbed from soil as nitrate or ammonium; needed for proteins 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; fungi enhance plant nutrient uptake.

Role of Bacteria and Fungi in Fertilizing Topsoil

Soil microorganisms play a crucial role in nutrient cycling and soil fertility.

• Bacteria: Some fix atmospheric nitrogen into forms plants can use (e.g., Rhizobium in legumes).

• Fungi: Decompose organic matter, releasing nutrients back into the soil.

Chapter 18: The Evolution of Invertebrate Diversity

Characteristics of Flatworms

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

• Body Plan: Flattened, soft-bodied, no body cavity (acoelomate).

• Digestive System: Incomplete or absent; some are parasitic.

• Examples: Planarians, tapeworms, flukes.

Characteristics of Arthropods

Arthropods are the most diverse animal phylum.

• Key Features: Segmented body, exoskeleton made of chitin, jointed appendages.

• Groups: Insects, arachnids, crustaceans, myriapods.

Distinctive Features of Chordates

Chordates (phylum Chordata) share several defining characteristics at some stage of development.

• Notochord: Flexible rod for support.

• Dorsal hollow nerve cord.

• Pharyngeal slits or clefts.

• Post-anal tail.

Relative Abundance of Invertebrates and Arthropods

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

• Invertebrates: Over 95% of all animal species.

• Arthropods: Most abundant and diverse, especially insects.

Chapter 19: The Evolution of Vertebrate Diversity

Defining Characteristics of Vertebrates

Vertebrates are chordates with a backbone (vertebral column).

• Features: Skull, backbone, complex organ systems.

• Groups: Fish, amphibians, reptiles, birds, mammals.

Ectothermic Animals

Ectotherms are animals whose body temperature depends on the environment.

• Examples: Reptiles, amphibians, most fish.

• Adaptations: Behavioral regulation of temperature (basking, seeking shade).

Distinguishing Traits of Mammals

Mammals are vertebrates with unique features.

• Hair: Provides insulation and protection.

• Mammary Glands: Produce milk to nourish young.

Characteristics of Most Fish

Most fish share certain anatomical features.

• Operculum: Bony flap covering and protecting the gills.

• Swim Bladder: Gas-filled organ for buoyancy control.

Distinguishing Features of Sharks and Rays

Sharks and rays are cartilaginous fish (class Chondrichthyes).

• Cartilage Skeleton: Flexible, lighter than bone.

• Other Features: Lack swim bladders, have exposed gill slits.

Characteristics of Tetrapods

Tetrapods are vertebrates with four limbs.

• Groups: Amphibians, reptiles, birds, mammals.

• Adaptations: Limbs for movement on land, lungs for breathing air.