Interactions Among Plant Systems Biology 10(B)

Interactions Among Plant Systems Learning objectives Identify major systems in plants Describe the interactions that occur among systems to carry out vital plant functions After this lesson you will be able to identify major systems in plants. You will also be able to describe the interactions that occur among these systems to carry out vital plant functions.

Plant Systems Organ systems: Tissue systems: Shoot system – above- ground Root system – below-ground Dermal Ground Vascular Tissues Shoot system Tissue systems: Dermal – barrier Ground – metabolic functions Vascular – transport Plant systems can be discussed on two levels: organs and tissues. Plants consist of two organ systems. The shoot system includes all above-ground organs, such as leaves, stems, and flowers. The root system includes all below-ground organs, or mainly roots. These organ systems are composed of three different types of tissue. The dermal tissue is the outer covering of the plant that serves as a protective barrier. Ground tissue is responsible for carrying out most of the plant’s metabolic functions, such as photosynthesis. Vascular tissue transports needed substances throughout the plant, such as food and water. Each plant organ contains of all three types of tissue. Root system

Interactions Among Plant Systems Organ and tissue systems interact to carry out vital functions Transport Reproduction Response While each system has its own unique functions, all organ and tissue systems interact to carry out many functions that are vital to the plant’s survival. Three functions that we will discuss in more detail are transport, reproduction, and response.

Transport Movement of needed materials throughout plant Major function of vascular tissue Xylem – transports water and minerals Phloem – transports glucose Both transport hormones Transport is the movement of needed materials throughout the plant. Needed materials, such as food and water, are produced or absorbed by a specific organ and must be transported to the rest of the organs to be used. Transport is carried out by two types of vascular tissue. Xylem transports water and minerals. Phloem transports food in the form of sucrose. Both types of vascular tissue transport hormones throughout the plant.

Interactions Among Plant Systems Interactions during transport Root system Absorbs water and minerals Shoot system Ground tissue produces glucose through photosynthesis Both organ systems Produce hormones Vascular tissue transports all materials throughout the plant Successful transport depends on interactions among several systems. The root system absorbs water and minerals. Ground tissue in the shoot system carries out photosynthesis to produce glucose. Both organ systems produce hormones. All of these needed substances are then transported throughout both organ systems by vascular tissue. These interactions ensure that all substances are delivered to the organs that need them.

Image by Roberto MM [GFDL] Reproduction Vegetative propagation – offspring produced from part of a plant organ Asexual Pollination – offspring produced via pollinated seeds Sexual In general, plants utilize two methods of reproduction. Plants can reproduce asexually by the process called vegetative propagation. In this type of reproduction, the offspring plant grows directly from an organ of the parent plant, such as a root or stem. The offspring plant is genetically identical to the parent plant. Plants can reproduce sexually by the process of pollination. In this type of reproduction, the offspring plant is produced by the combination of a male and female gamete into a pollinated seed. This process produces a completely independent offspring plant whose genetic makeup is a result of the gametes that were combined. A common example of this occurs in flowering plants. Image by Roberto MM [GFDL]

Reproduction by Pollination Flower – organ that produces seeds Seed – fertilized ovule (embryo) and stored food (cotyledon) surrounded by a protective seed coat The flower is the plant’s reproductive organ. Flower structure differs slightly, but in general a flower contains several male stamen and a single, larger female pistil. When pollen from a stamen is transferred to the ovule of the pistil, pollination has occurred. A fertilized seed is produced, and a fruit develops around it. The entire process is regulated by hormones. A seed consists of three major structures. The embryo is the fertilized ovule produced during pollination. The cotyledon stores food for the developing plant. Both structures are surrounded by a protective seed coat that allows the seed to retain moisture. Fruit – develops around fertilized ovule(s)

Interactions Among Plant Systems Interactions during reproduction Vegetative propagation Shoot and root systems: part of an organ produces a new plant Pollination Shoot system: flowers are the site of seed pollination and fruit development Shoot and root systems: produce hormones, transported by the vascular tissue, that regulate flower budding, fruit ripening and seed growth Successful reproduction depends on interactions among several systems. In vegetative propagation, an entirely new shoot and root system grows from part of an organ from a parent plant. In pollination, the flowers of the parent plant’s shoot system are the site of seed pollination and fruit development. Important steps in the reproductive process, such as flower budding, fruit ripening, and seed growth are regulated by hormones. Remember that the shoot and root systems both produce hormones. These hormones are transported to flowers by the vascular tissue. These interactions ensure the best chances of producing viable offspring.

Response Tropisms – plant’s hormonal growth response toward or away from an external stimulus Examples: Phototropism – stem and leaves grow toward a light source Positive gravitropism – roots grow toward gravity (downward) Negative gravitropism – stem and leaves grow away from gravity (upward) Response is a plant’s ability to react to changes in its environment. Tropisms are a type of response in which hormones signal a plant to grow toward or away from a stimulus in the environment. Examples of common plant tropisms include phototropism and gravitropism. In phototropism, a plant’s stem and leaves grow toward a light source. This allows the plant to gain the greatest possible exposure to the light energy needed for photosynthesis. In positive gravitropism, a plant’s roots grow toward gravity. This increases the plant’s likelihood of finding water. In negative gravitropism, a plant’s stem and leaves grow away from gravity. This increases the plant’s chances of finding light.

Interactions Among Plant Systems Interactions during response Root system Grows toward gravity Shoot system Grows toward light and/or away from gravity Both systems Produce hormones Transported hormones Successful response depends on interactions among several systems. The root system grows toward gravity to seek water. The shoot system grows toward light and away from gravity to seek light energy for photosynthesis. These growth responses are all stimulated by hormones produced in both organ systems. You will recall that hormones are transported to the sites of cell growth by the vascular tissue. These interactions ensure that the plant is able to obtain needed materials from the environment.

Interactions Among Plant Systems Learning objectives Identify major systems in plants Describe the interactions that occur among systems to carry out vital plant functions You should now be able to identify major systems in plants. You should also be able to describe the interactions that occur among these systems to carry out vital plant functions.