Comparison of Plant vs. Animal Development

Plant

Respond by physiological adjustment

Cell divisions contribute to de novo formation of organs all the way through to senescence

Growth is serial, repetitive, and plastic

No reserved germline

More tolerant of genetic abnormalities

Embryos simple and complete

Plant cells are totipotent

Cellulose boxes bulging with water filled balloons

Animal

Cells and organisms move

Cell division serves to regenerate and maintain tissues and circulating cell populations

Growth is concurrently repetitive

Reserved germline set aside in embryogeny

Low tolerance to genetic abnormalities

Embryos complex and incomplete

Essentially no asexual propagation

No cell wall

Life is manifested in growth. In plants, growth can be of two types, heterotrophic and autotrophic.

Autotrophic growth uses inorganic material for nourishment.
Heterotrophic growth is dependent on organic material for nourishment.

During germination, seedlings usually grow heterotropically but once a plant becomes photosynthetic it can grow autotrophically - using minerals from the soil and atmosphere and sunlight for energy. Thus, for most of their life plants are autotrophic. However, there are some parasitic plants that grow heterotropically, obtaining inorganic material from their host.

Some basic aspects for autotrophic growth are:

Synthesis of organic substances from inorganic elements and light.

Development of structures for securing inorganic elements and light (vegetative growth.

Production of more individuals (reproductive growth).

These are interrelated since biosynthesis is needed to make more plant structures (more plant cells, tissues, organs) to exploit the environment and reproduce.

Biosynthesis involves accumulating diffuse oxidized elements (nutrients) from the environment, and reducing and bonding them into concentrated forms (complex molecular structures like proteins)- schematically depicted below:

Some general levels of growth control in plants include

Environmental - supply of requisites and sensory information

Genetic - determine what is synthesized via enzymes

Hormonal - regulation of gene expression and biosynthesis

To study plant growth and development, it is important to have knowledge of plant cell structure and function.

Plants produce maximum absorbing surface/volume of cytoplasm by having many cells. As plant cells grow, they make a thin layer of cytoplasm and a large vacuole:

cell surface varies as square of radius (4 r²)

cell volume varies as cube (4/3 r³)

Cells must have:

protective and strengthening structures (walls) boundary structures for in-and-out traffic (membranes)

structures for converting light to chemical energy (chloroplast)

structures for oxidizing carbohydrate to produce energy (mitochondria)

structures for synthesizing enzymes (ribosomes)

structures for biosynthesis (enzymes)

structures for reproduction (nucleus)

etc.

Tissues and organs, which are made of cells, are organized for maximum interception of environmental requisites. Since plant tissues and organs are separated in space there must be connective tissues for support and conduction.

Maximum growth requires occupancy of the largest possible volume of environment, which, in turn, requires coordination of root-shoot activities and growth so as to balance H2O and nutrient ion supply with light and CO2 supply.

For example:

Thin, flat or needle-like leaves with minimum overlap for light absorption.

Supporting tissues (branches) for displaying leaves in space.

Conductive tissues for transport of food, water and signals.

Growth organized to put new leaves into surrounding space.

Thin cylindrical roots that can be forced through soil.

Extensive root branching for maximizing absorption at surface.

Reproductive growth is parasitic so reproduction must be timed to occur when vegetative structure can support the drain on energy and materials. Mechanisms are required to assure pollination and fertilization, and to shift metabolic economy from vegetative to reproductive growth. Specific structures and physiology are required to secure seed survival during periods of adverse environments (dormancy).

Growth and development involves ontogeny (sequential developmental stages during growth controlled by endogenous genetic programs) and phenology (relationship between annual cyclic changes in environment and plant growth and development).

Adaptation to different environments.

Plants can be found in almost every type of environment the earth provides, even under extremes of temperature, moisture, light, growing season, etc. Adaptation to the extremes involves specialized structures and metabolism.

Examples of environmental adaptations:

The process of dormancy ensures survival of adverse environments by the capacity to NOT grow, but to retain viability. For winter survival of seeds, the seed embryo is prevented from germinating during seed formation and maturation (controlled by hormones). The seed then dries out and remains in dormant state until the hormonal inhibition is broken, after which, germination becomes possible when the environment becomes favorable.

Succulent cacti of deserts conserve water by only opening their stomates for gas exchange at night when evaporation is minimal. During the night they absorb and trap CO₂. During the day when the stomates are closed and light is available the CO₂ is used for photosynthesis.

Relation to applied plant sciences

The study of plant growth and development has contributed much information utilized by modern applied plant sciences, such as agronomy, forestry, horticulture and plant pathology. Examples are found in mineral nutrition, weed control, flowering, propagation, irrigation, tissue cultures, etc. Plant biologists often find employment in a variety of horticultural and agronomic careers and as parts of research programs in applied plant sciences at universities, government agencies, and industry.

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