Speciation, Extinction & Taxonomy

• Speciation signifies the formation of new species.
• Extinction marks the termination of a species.

Key Concepts of Species and Taxonomy

• Species are defined as organisms capable of interbreeding and producing fertile offspring.
• Taxonomy is the science devoted to the classification, identification, and naming of organisms.
• Classification categories, from broadest to narrowest, are: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.

Systematics and Phylogenetic Trees

• Systematics involves the scientific study of organismal diversity and their evolutionary connections.
• A phylogenetic tree is a diagram illustrating evolutionary relationships among species, often based on shared traits or genetic data.
• Branch junctions in a phylogenetic tree denote a shared common ancestor.

Cladistics and Clades

• Cladistics uses shared derived characteristics (synapomorphies) to construct phylogenetic trees.
• Phylogenetic trees are subject to change as new data from fossils or genetic information emerges.
• A clade is a group containing a common ancestor and all its descendants, characterized by shared derived traits.

Molecular Systematics

• Molecular Systematics employs molecular data like DNA, RNA, and protein sequences to explore evolutionary relationships.
• Genetic comparisons can reveal relationships between species (e.g., humans and other primates).

Major Plant Groups

• Nonvascular plants (bryophytes), such as mosses, liverworts, and hornworts, lack vascular tissue, are small, and thrive in moist environments.
• Seedless vascular plants, like club mosses and ferns, possess vascular tissue and reproduce through spores.
• Seed plants, including gymnosperms (e.g., pines) and angiosperms (e.g., roses), produce seeds and have vascular tissue.

Monocots vs. Eudicots

• Monocots have one cotyledon, while eudicots have two.
• Monocots exhibit parallel leaf venation, whereas eudicots display a net-like pattern.
• Monocot flower parts occur in multiples of three, and eudicot flower parts appear in multiples of four or five.

Root and Shoot Systems

• The root system anchors the plant and absorbs water and nutrients, comprising primary root, lateral roots, root hairs, root cap, and vascular tissue.
• The shoot system, consisting of stems, leaves, and flowers, is above-ground and supports photosynthesis and reproduction.
• Roots absorb nutrients, stems provide support and transport, and leaves carry out photosynthesis.

External Shoot Structures

• The shoot system incorporates structures like the terminal bud, axillary bud, nodes, and internodes to facilitate growth and reproduction.
• Terminal buds are situated at the stem tip, driving primary growth and apical dominance.
• Axillary buds, found where leaves meet the stem, can develop into new branches or flowers upon terminal bud removal.
• Terminal (apical) buds are at the stem tip, controlling elongation and producing growth hormones.
• Axillary buds, located above a node, can produce lateral growth when stimulated.
• Nodes mark attachment points for leaves and buds and are crucial for branching.
• Internodes are sections between nodes, supporting vertical growth and leaf spacing.
• Terminal bud growth is evident in young plants reaching for sunlight.
• Axillary buds sprout into branches when the main shoot is pruned.

Dermal Tissue

• Dermal tissue covers and protects the plant, including structures such as the cuticle, epidermis, stomata, and guard cells.
• The cuticle, a waxy layer on leaves and stems, waterproofs the plant.
• The epidermis is a single cell layer providing protection.
• Stomata are tiny openings for gas exchange, essential for photosynthesis and respiration.
• Guard cells regulate stomatal opening and closing, managing water loss.

Ground Tissue

• Ground tissue makes up most non-woody plant parts and is involved in roles such as photosynthesis, storage, and support.
• Parenchyma cells are thin-walled and flexible, participating in photosynthesis and storage.
• Collenchyma cells have unevenly thickened walls, providing support in young stems.
• Sclerenchyma cells are thick-walled, offering strength and protection, and contain lignin.

Vascular Tissue

• Vascular tissue is responsible for transporting water, minerals, and sugars throughout the plant.
• Xylem consists of hollow tubes that transport water and minerals, composed of dead cells at maturity.
• Phloem transports sugars and nutrients, made up of living cells, including companion cells and sieve-tube elements.

Root Structures

• The root cap protects the root tip and assists in soil movement.
• Root hairs expand the surface area for absorption.
• The epidermis protects the root and regulates uptake.
• The cortex stores food and transports water.
• The endodermis regulates nutrient movement into vascular tissue.
• The pericycle gives rise to lateral roots.

Monocot vs. Eudicot Roots

• Monocot roots exhibit xylem and phloem forming a ring, a large cortex, and a present pith, without secondary growth.
• Eudicot roots have xylem forming a central star, a smaller cortex, an often-absent pith, and frequently undergo secondary growth.

Stem Structures and Functions

• Monocots have scattered vascular bundles; eudicots have them arranged in a ring.
• Monocots lack distinct cortex and pith; eudicots possess both.
• Monocots do not undergo secondary growth; eudicots often experience it.
• Monocots include corn and bamboo; eudicots include roses and oak trees.
• Ground tissue in monocot stems offers undifferentiated support and storage.
• The cortex in eudicot stems stores nutrients and transports water to vascular tissues.
• The pith in eudicot stems is central, storing and transporting nutrients.
• Rhizomes are underground stems used for storage and vegetative reproduction (e.g., ginger).
• Tubers are swollen stems for starch storage (e.g., potatoes).
• Bulbs are short stems with fleshy leaves for food storage (e.g., onions).
• Stolons are above-ground runners for vegetative reproduction (e.g., strawberries).
• Thorns protect from herbivores (e.g., honey locust).
• Tendrils aid in climbing (e.g., grapevines).

Leaf Structures and Functions

• The blade captures sunlight for photosynthesis.
• The petiole connects the leaf to the stem and transports nutrients.
• Veins transport water and nutrients within the leaf.
• Palisade mesophyll contains chloroplasts for photosynthesis.
• Spongy mesophyll facilitates gas exchange with air spaces.
• Monocots have parallel venation; eudicots have net-like venation.
• Monocots lack distinct mesophyll layers; eudicots have palisade and spongy layers.
• Stomata in monocots are evenly distributed; in eudicots, they're mostly on the lower surface.

Deciduous vs. Evergreen Leaves

• Deciduous leaves shed seasonally, adapting to water loss (e.g., maples).
• Evergreen leaves remain year-round, often with a waxy coating to reduce water loss (e.g., pines).

Growth and Development

• Meristems are regions of active cell division in plants.
• Primary growth increases length; secondary growth increases thickness.
• Shoot apical meristems are at stem tips; root apical meristems are at root tips.
• Vascular cambium produces secondary xylem (wood) and phloem.
• Cork cambium produces cork, which protects the plant.
• Wood consists of xylem; bark consists of phloem and cork.
• Wood is located inside the bark in woody plants.
• Secondary growth occurs through vascular cambium activity, producing new xylem and phloem layers.

Plant Nutrition and Transport

• The Casparian strip in roots controls water and solute uptake.
• The cohesion-tension mechanism moves water through plants via transpiration.
• Plants conserve water through structures like waxy cuticles and stomata regulation.
• The pressure flow mechanism moves sugars from sources to sinks in phloem.
• Water follows solutes, aiding in sugar transport.

Reproduction and Development of Flowering Plants

• Male structures: anther (produces pollen), filament (supports anther).
• Female structures: stigma (receives pollen), style (connects stigma to ovary), ovary (contains ovules).
• Microspores develop into haploid pollen grains.
• Pollen grains include generative and tube cells, yielding sperm and the pollen tube, respectively.
• Megaspores develop into haploid embryo sacs.
• Embryo sacs contain egg cells and synergids, which participate in fertilization.
• Pollination occurs through wind, insects, or animals; double fertilization results in a zygote and endosperm formation.
• The endosperm nourishes the developing embryo.