Personal notes for RHS Level 2 Certificate in the Principles of Plant Growth and Development
Unit 1: Plant Science 1: Internal Plant Structures: AO1 - AO2
The diagram illustrates a simplified stem followed by a close-up of the different layers.
Working from outer to inner tissues we begin with the epidermis, a protective, single layer, which produces an outer wax layer of cuticle call cutin, which is waterproof. Punctuating the epidermis layer are stomata pores, allowing gases to pass through the otherwise impermeable layer.
Underneath the epidermis is the cortex, largely constructed of unspecialised parenchyma tissue. These thin-walled cells are held in an approximately spherical shape by osmotic pressure, with many air spaces between them. This mass of cells also combines to assist with maintaining the plant shape, in addition to other functions, such as containing chlorophyll and releasing energy via respiration for use by surrounding tissues. In some plants, they can act as food stores, as in potato tubers.
Phloem and Xylem are the two vascular bundles within plant stems:
Phloem, containing long, tube-like cells, is responsible for transporting organic nutrients (such as sugars) from the leaves to other areas of the plant.
Xylem, containing long, wide, and open-ended cells with thick lignified walls, is the dead, permanent tissue located at the centre of the vascular bundle. It transports water and dissolved minerals from the roots to other plant parts.
In dicotyledons resides the vascular cambium, a lateral meristem which contains actively dividing cells that produce more phloem and xylem tissue. This increases the girth of the stem in woody plants and is known as secondary thickening. The bundles are arranged in a ring providing both strength and support.
Working from outer to inner tissues we begin with the epidermis, a protective, single layer, which produces an outer wax layer of cuticle call cutin, which is waterproof. Punctuating the epidermis layer are stomata pores, allowing gases to pass through the otherwise impermeable layer.
Underneath the epidermis is the cortex, largely constructed of unspecialised parenchyma tissue. These thin-walled cells are held in an approximately spherical shape by osmotic pressure, with many air spaces between them. This mass of cells also combines to assist with maintaining the plant shape, in addition to other functions, such as containing chlorophyll and releasing energy via respiration for use by surrounding tissues. In some plants, they can act as food stores, as in potato tubers.
Phloem and Xylem are the two vascular bundles within plant stems:
Phloem, containing long, tube-like cells, is responsible for transporting organic nutrients (such as sugars) from the leaves to other areas of the plant.
Xylem, containing long, wide, and open-ended cells with thick lignified walls, is the dead, permanent tissue located at the centre of the vascular bundle. It transports water and dissolved minerals from the roots to other plant parts.
In dicotyledons resides the vascular cambium, a lateral meristem which contains actively dividing cells that produce more phloem and xylem tissue. This increases the girth of the stem in woody plants and is known as secondary thickening. The bundles are arranged in a ring providing both strength and support.
Pith refers to the central zone of the stem, mainly made up of parenchyma cells. These can break down to leave a hollow stem.
There are two final cells to mention in this section, collenchyma and sclerenchyma:
Collenchyma provides extra mechanical and structural support, especially in regions of new growth. It helps young stems and leaves maintain their shape and withstand bending forces.
Sclerenchyma provides the main structural support to a plant. Unlike collenchyma, mature sclerenchyma cells are generally dead at maturity.
Thanks for sharing the diagrams and the information. I need to brush up on the terminology, and this is helpful.
ReplyDeleteThanks Beth! This is my way of trying to brush up - it's been a while since I've studied plants.
Delete