A Plant Process Animation: Photosynthesis

A Plant Process: Cellular Respiration

Cellular respiration, also referred to as oxidative metabolism, is a set of metabolic processes and reactions executed within the cell of an organism in order to convert the biochemical energy, derived from the nutrients, to adenosine triphosphate (ATP). ATP is a nucleotide which is the major source of energy for cellular reactions. The process revolves around catabolic reactions which facilitate oxidation of one molecule, with the reduction of the other. There are two types of cellular respiration, aerobic cellular respiration and anaerobic cellular respiration. Both, animals as well as plants, execute cellular respiration to produce energy. They use nutrients such as glucose, amino acids, and fatty acids to produce the energy. The common oxidizing agent in this process is molecular oxygen.

A Plant Process: Photosynthesis

Photosynthesis is the process of converting light energy to chemical energy and storing it in the bonds of sugar. This process occurs in plants and some algae (Kingdom Protista). Plants need only light energy, CO₂, and H₂O to make sugar. The process of photosynthesis takes place in the chloroplasts, specifically using chlorophyll, the green pigment involved in photosynthesis. 

Photosynthesis takes place primarily in plant leaves, and little to none occurs in stems, etc. The parts of a typical leaf include the upper and lower epidermis, the mesophyll, the vascular bundle(s) (veins), and the stomates. The upper and lower epidermal cells do not have chloroplasts, thus photosynthesis does not occur there. They serve primarily as protection for the rest of the leaf. The stomates are holes which occur primarily in the lower epidermis and are for air exchange: they let CO₂ in and O₂ out. The vascular bundles or veins in a leaf are part of the plant's transportation system, moving water and nutrients around the plant as needed. The mesophyll cells have chloroplasts and this is where photosynthesis occurs. 

Seed Plants

Seed plants are heterosporous- they have 2 different spore sizes: megaspores and microspores.
The generalized life cycle of plants has been modified to illustrate plants which have separate male and female gametophytes produced by different sized spores.

The evolutionary trend from nonvascular plants to seedless vascular plants to seed plants has been a reduction in the size of the gametophyte. In seed plants, the gametophyte is usually microscopic and is retained within the tissues of the sporophyte.

The megasporangium is surrounded by layers of sporophyte tissue called the integument. The integument and structures within (megasporangium, megaspore) are the ovule.

Microspores germinate within the sporophyte tissue and become pollen grains. The microgametophyte is contained within the tough, protective coat of the pollen grain.

The entire pollen grain is transferred to the vicinity of the pollen grain by a process of pollination. Wind or animals usually accomplish this transfer.

When pollen reaches the female gametophyte, it produces an elongate structure (pollen tube) that grows to the egg cell. Sperm are transferred directly through this tube to the egg. The advantage of this process is that sperm do not have to swim long distances as they do in seedless plants.

Seedless Plants

The Seedless Vascular Plants consist of four main Divisions; Pterophyta (ferns), Psilophyta, Lycophyta, and Sphenophyta.  These plants all share the common evolutionary trait of vascular tissue; specialized transport tissue found in most "modern" plants.  This means the plant can now transport water and soil nutrition more efficiently allowing for greater complexity in plant structure including height and the ability to support a more complex structure of photosynthesis, leaves. Xylem and phloem, the two major types of vascular tissue, each transport water and nutrition, respectively, to the upper regions of the plant from the root system.  The Vascular Seedless plants are the most evolutionarily advanced plants aside from the seeded plants.