General Biology 2 (Term 1) - Grade 12

Homologous Structures

Structures with similar anatomy and embryonic origin but different functions.

Analogous Structures

Organisms living in similar environments may independently evolve similar features despite having different evolutionary origins.

Convergent evolution

It is when unrelated species independently evolve similar physical traits or behaviors because they live in similar environments or face the same survival challenges.

Vestigial Structures

They are reduced or nonfunctional body parts inherited from ancestors.

Embryology

Embryonic development reveals similarities among organisms that may not be obvious in adulthood.

Systematics

The study of organisms with the purpose of deriving their relationships.

Phylogeny

It is the evolutionary history and the relationships among a species or group of species.

Phylogenetic relationships

They provide information on shared ancestry but necessarily on how organisms are similar or different.

The Phylogenetic Tree

A tool scientists use to show the evolutionary pathways and connections among organisms. It is considered to be a hypothesis of the evolutionary past since one cannot go back to confirm the proposed relationships.

The Classic Model

This model of a phylogenetic tree is a branching diagram rooted in a single common ancestor that represents species diverging via vertical descent. It represents the last universal common ancestor (LUCA) from which all life descends.

Horizontal Gene Transfer (HGT)

The introduction of genetic material from one species to another species by mechanisms other than the vertical transmission from parent(s) to offspring. These transfers allow even distantly related species to share genes, influencing their phenotypes.

Genome Fusion and the Evolution of Eukaryotes

Scientists believe the ultimate in HGT occurs through genome fusion between different species of prokaryotes when two symbiotic organisms become endosymbiotic. This occurs when one species is taken inside the cytoplasm of another species, which ultimately results in a genome consisting of genes from both the endosymbiont and the host.

Web and Network Models

In 1999, W. Ford Doolittle proposed a phylogenetic model that resembles a web or a network more than a tree. The hypothesis is that eukaryotes evolved not from a single prokaryotic ancestor, but from a pool of many species that were sharing genes by HGT mechanisms.

Ring of Life Model

A phylogenetic model where all three domains of life evolved from a pool of primitive prokaryotes. Proposes a ring-like model in which species of all three domains—Archaea, Bacteria, and Eukarya— evolved from a single pool of gene-swapping prokaryotes.

Shoot system

An organ system of a vascular plant’s body that includes stems, leaves, and reproductive organs (flowers, fruits, seeds)

Root system

An organ system of a vascular plant’s body that often serve to anchor the plant in soil.

Meristematic Tissue

Cells of this type of tissue are found in meristems, which are plant regions of continuous cell division and growth. This tissue cells are either undifferentiated or incompletely differentiated.

Apical meristems

They contain meristematic tissue located at the tips of stems and roots, which enable a plant to extend in length.

Lateral meristems

They facilitate growth in thickness or girth in a maturing plant.

Intercalary meristems

They occur only in monocots at the bases of leaf blades and at nodes (the areas where leaves attach to a stem. This tissue enables the monocot leaf blade to increase in length from the leaf base.

Permanent (non-meristematic) Tissue

Consists of plant cells that are no longer actively dividing. Cells that are produces from meristems that quickly differentiate, or specialize, and become permanent tissue.

Dermal tissue

A protective layer that covers the outer surfaces of plants, consisting of the epidermis and, in some cases, additional cell layers such as the periderm in woody plants. It serves to protect against water loss, pathogens, and physical damage while also allowing for gas exchange.

Epidermis

The outermost layer of cells in plants that acts as a protective barrier. It functions to prevent water loss, protect against pathogens, and minimize physical damage while also allowing for gas exchange through specialized structures such as stomata. It may have additional adaptations like a waxy cuticle to further reduce water loss and improve resilience.

Stomata

Small openings on the surface of leaves and stems that allow for the exchange of gases between the plant and its environment. They play a crucial role in photosynthesis by enabling carbon dioxide to enter and oxygen to exit. It also helps regulate water loss through transpiration, and their opening and closing are controlled by surrounding guard cells in response to environmental conditions such as light, humidity, and CO2 levels.

Vascular tissue

A complex tissue responsible for the transport of water, minerals, and sugars throughout the plant. It consists of various cell types and is primarily composed of two specialized conducting tissues: xylem and phloem. This system is essential for plant growth, nutrient distribution, and overall physiological

Xylem tissue

It transports water and nutrients from the roots to differed parts of the plant. It is composed of tracheids and vessel elements, which are dead at maturity and form hollow tubes.

Phloem tissue

It transports organic compounds from the site of photosynthesis to other parts of the plant. It is made of living cells, like sieve tube elements and companion cells.

Ground tissue

It serves as a site for photosynthesis, provides a supporting matrix for vascular tissue, and helps to store water and sugars.

Parenchyma

A type of plant tissue that is involved in various essential functions such as photosynthesis, storage of nutrients and water, and tissue repair. These cells are typically thin-walled and can be found in many parts of the plant, including leaves, stems, and roots. They play a vital role in metabolic processes and can also differentiate into other cell types to aid in healing after damage.

Collenchyma

It is a living plant tissue composed of elongated cells with unevenly thickened primary cell walls. It provides flexible mechanical support, tensile strength, and elasticity to growing plant organs like young stems, leaf petioles, and veins without restricting their growth.

Sclerenchyma

It is a rigid, supportive plant tissue made of dead cells with thick, woody walls containing lignin. It gives strength and hard structure to mature parts of plants like stems, seed coats, and nut shells.

Root

It is an organ that anchors a vascular plant in the soil, absorbs minerals and water, and often stores carbohydrates and other reserves

Taproot

In eudicots, it is an enlarged primary root together with all of the lateral roots that branch from it. In this system, the role of absorption is restricted largely to the tips and facilitates the anchorage of the plant in sol by preventing toppling.

Fibrous root

Composed of an extensive mass of similar-sized adventitious roots; typical of monocots. It stays close to the soil surface to quickly absorb surface water.

Indeterminate growth

It is when growth continues as long as the plant lives.

Annuals

They complete their life cycle in a single year or less.

Biennials

They generally require two growing seasons to complete their life cycle.

Perennials

They live many years.

Primary Growth

This is the lengthening of roots and shoots. Occurs at apical meristems (tips of roots and shoots). It is responsible for vertical growth.

Zone of cell division

It is located near the tip of the root. It is composed of the apical meristem and its derivatives (primary meristem).

Zone of elongation

Cells elongate to at least 10x their original length. It pushes the root tip through the soil. Continued growth is sustained by the meristems addition of new cells to the youngest end of the elongation zone.

Zone of maturation

Farthest from the root tip. Cells in this region become specialized in structure and function.

Branching of shoots

It is part of primary growth which rises from the activation of axillary buds.

Secondary Growth

It is the increase of thickness. Occurs in woody plants. Driven by lateral meristems, like the vascular cambium and cork cambium. Produces secondary xylem (wood) and secondary phloem.

Annual Tree Rings

Result from seasonal differences in xylem cell size during secondary growth.

Stem

It is a plant organ bearing leaves and buds. It is the main axis of the plant that bears all structures above the ground. Its chief function is to elongate and orient the shoot in a way that maximizes photosynthesis by the leaves. It has alternating system of nodes and internodes.

Leaves

Lateral outgrowths that develop from the node of the stem. Main photosynthetic organ of the plant. Other functions include intercepting light, exchange gases with the atmosphere, dissipate heat, and defense from herbivores and pathogens.