Roots

Distinguish between a primary root vs a lateral/branch root.

Primary root: originates directly from the embryonic root or radicle. This root grows in the downward direction into the soil. Lateral roots: extend horizontally from the primary root (radicle) and serve to anchor the plant securely into the soil. This branching of roots also contributes to water uptake, and facilitates the extraction of nutrients required for the growth and development of the plant.

What are the four primary functions of roots?

A root's four major functions are 1) absorption of water and inorganic nutrients (e.g. nitrogen, phosphorous, calcium) 2) anchoring of the plant body to the ground, and supporting it 3) storage of food and nutrients (e.g. carbohydrates) 4) transport and conduction of water, (some) hormones, and minerals to the stem.

Adaptations in roots for oxygen: arenchyma and pneumatophores: what are these and what type of habitats do plants with these adaptations occur in?

Arenchyma: parenchyma tissue with greater amounts of air space - an adaptation in plants growing in wetlands, especially herbaceous species Pneumatophores: "air roots" -gets O2 to the plants root system especially in woody species

Root anatomy and terms: For all of the below, be able to name which tissue system they belong to ~ epidermis, cortex, pith, endodermis, exodermis, pericycle, xylem, phloem. What is the function of each?

Epidermis: offers protection, thin layer of cells Cortex: comprised of parenchyma -usually for storage of nutrients -contains a lot of leucoplasts -air spaces in cortex for gas exchange Pith: extra layer of ground tissue (parenchyma) laying below the vascular tissue **found in monocot roots Endodermis: inner most layer of cortex -surrounds the vascular tissue/cylinder -contains the caspian strip in the cell wall to regulate water flow into the cell and move through the roots via plasmodesmata **helps defend against pathogens and toxins by only allowing permeable substances through the plasma membrane ** puts stops to apoplastic transport Exodermis: suberin deposits -prevents water absorption -in inactive portions of the roots to protect against pathogens Pericycle: 1 cell thick layer of parenchyma cells Xylem Phloem

Why do some plants form root nodules?

Found primarily in the legume family -nitrogen fixing bacteria are housed within the nodule -plants exude chemicals to attract bacterial colonization -often pink due to presence of leghemoglobin - regulates the concentration of oxygen in the nodule to promote maximum nitrogen fixation ** in the presence of excess oxygen, nitrogen cannot bind.

Where do branch (lateral) roots originate from? What is the purpose of them originating from here?

Lateral roots originate from from this primary meristem tissue. In plants undergoing secondary growth, the pericycle contributes to the vascular cambium often diverging into a cork cambium. Each lateral root can differentiate and grow additional lateral roots Primary roots arise from the radical (embryonic root)

What takes place in the region of cell division, cell elongation, and cell maturation? In which region are root hairs found and why?

Region of cell division: active cell division -formation of meristematic tissues ** no elongation here Region of cell elongation: cellular elongation pushes root tips forward through the soil -formation of some matured tissues here Region of cell maturation: fully formed tissues (ground tissue, dermal tissue, and vascular tissue) - formation of root hairs **root hairs increase surface area to allow more nutrient and water absorption ** do not regenerate after they have sloughed off

Why are root hairs important?

Root hairs form an important surface over which plants absorb most of their water and nutrients

Distinguish between a taproot vs. fibrous root system and which plants are most likely to have each.

Taproot system: main root of a primary root system, growing vertically downward. Most dicotyledonous plants (see cotyledon), such as dandelions, produce taproots, and some, such as the edible roots of carrots and beets, are specialized for food storage. fibrous root system: is the opposite of a taproot system. It is usually formed by thin, moderately branching roots growing from the stem. A fibrous root system is universal in monocotyledonous plants and ferns.

Why do tropical trees have shallow root systems?

Most rainforest soil is very poor with all the nutrients available largely remaining at surface level. Because of this rainforest trees have very shallow roots so that they can absorb nutrients before heavy rainfall pushes the nutrients below the surface and too deep into the ground to absorb. These extended roots also increase the area over which nutrients can be absorbed from the soil, which helps in the heavily competitive rainforest floor.

What role do mycorrhizal fungi play in plant growth? Distinguish between ecto vs. endomycorrhizal fungi.

Mycorrhizal fungi colonize the root system of a host plant, providing increased water and nutrient absorption capabilities while the plant provides the fungus with carbohydrates formed from photosynthesis. a) ectomycorrhizal fungi grow on the surface of the plant b) endomycorrhizal fungi penetrate the cell and grow internally

What are the various functions of the root cap and mucigel?

Root cap: protects cells from soil/ground damage so they can continue to differentiate and grow Mucigel: cytoplasm from sloughed off cells, -helps lubricate and penetrate the soil -binds soil to the roots -mobilizes soil nutrients -attracts beneficial soil microbes and fungi

Why do roots need oxygen? Do they need carbon dioxide?

Roots do need air (roots absorb oxygen primarily through root hairs) because the plant (mitochondria) needs oxygen for cellular/overall metabolism. Plants also metabolize sugars and require oxygen to do this. They do not need CO2 as they do not photosynthesize (lacks chlorophyl)in the roots.

Define adventitious roots.

Roots that are produced on the internodes or other parts of plant organs (stems and leaves) above the soils surface. -prop roots in corn -hold vines to substrate -means of vegetative reproduction -helpful in woody plants for air layering

What are the dominant cells in root cortex/pith?

The dominant cells in root cortex and pith are parenchyma cells

Which of the above has the casparian strip? What is this strip made of and what is its function?

The endodermis contains the caspian strip in the cell wall to regulate water flow into the cell and move through the roots via plasmodesmata. This helps defend against pathogens and toxins by only allowing permeable substances through the plasma membrane and puts a stop to apoplastic transport

What is the rhizosphere?

The soil region close to plant roots and characterized by a high level of microbiological activity. -Zone of soil that adheres to plant roots -Root cells secrete organic molecules, enrich region -Particular bacterial species appear to preferentially interact with certain plants