Plant roots and shoots Flashcards
When were roots first found?
Over 400 million years ago. Required to take up nutrients from the soil.
Function of the roots?
Roots form the interface between the plant and soil. Takes up nutrients and water. Anchor the plant. Interacts with soil microflora (rhizobium for nitrogen fixation)
What is found around the root?
Regions of dryness. As the plant takes up water from the soil Water moves down the gradient towards the roots, by osmosis. Aquaporins in the plasma membrane create a channel through which water can diffuse. Selective for water molecules due to its narrow diameter and hydrophobic nature which excludes charged molecules. Water can also diffuse through the plasma membrane by simple diffusion - less efficient.
What is hydrotropism?
Roots preferentially grow into the moist regions of the soil, as they can sense the moisture content of soil.
Why do different species have different root architecture?
Controlled by genes.
What else diffuses through the root membrane?
Nitrogen - important during leaf development of cereals Potassium - required during growth Phosphorus - in high demand during root system and seed development Magnesium - for chlorophyll
Diversity and evolution of root systems?
Liverworts - consists of a dense mass of multicellular rhizoids Mosses - dense mass of multicellular rhizoids. Increases root surface area so more nutrients and water can be taken up Evolution of a lignified water transport system after the mosses/hornworts. Evolution of a different type of roots in lycophytes.
How do roots form?
Cells at the basal region of the embryo form a root meristem. The root meristem is activated at germination to produce a primary root. The root system develops from the branching of the primary root. There are variations to this, such as maize which creates subsidary roots which develop further to make a thick brace root to stabilise the plant.
Does root growth have a determined end?
No, like shoots, but unlike leaves, flowers and fruits. Lateral roots originate from an internal tissue. The tip is covered with a root cap.
Root structure?
Differentiation zone between tip growth and hair initiation. Zone where cells differentiate, no cell growth except root hairs Elongation zone. Cells expand rapidly, without cell division Merisitemic zone. Stem cells of the root and actively dividing cells are located in the meristem Root cap & Columella. Protective tissues that secrete mucilage into the soil as protection.
What is the dermal tissue?
Hairs develop from this layer. Anchorage, nutrient uptake and interaction with microorganisms.
What is the vascular tissue?
Xylem and Phloem are located here.
Pericycle is a cell layer in the endodermis.
Solutes move into endodermal protoplast on the way to the xylem. Solutes and water move from the intercellular spaces of the ground tissue into the endodermis and from there to the xylem.
A water-resistant band (Casparian strip) stops solute and water movement through intercellular space around the endodermis.
Where do roots proliferate?
In regions where nutrients are abundant. Roots sense presence of nutrients, so when in an area of high concentration, the growth of roots increases in that region.
How do you determine sites of productivity?
Measure the amount of chlorophyll in a given area. The shoot systems present large surface areas to incoming sunlight.
The shoot systems support leaves which have a large surface area. Allows them to intercept sunlight for photosynthesis.
Gas exchange also occurs in the leaves.
Stem cells during embryogenesis of plants?
Shoot stem cells and root stem cells.
Organogenesis occurs in meristems: groups of dividing cells containing stem cells.
Shoots, leaves and flowers originate in the shoot stem cells.
