Chapter 3: Plant tissue Flashcards
What is mitosis
a process where a single cell divides into two identical daughter cells
What is plant tissue
a collection of similar cells performing an organised function for the plant
What is photosynthesis
The process in which green plants and some other organisms use sunlight to synthesize nutrients from carbon dioxide and water. Photosynthesis in plants generally involves the green pigment chlorophyll and generates oxygen as a by-product.
What does intracellular mean
The communication between cells or substances inside the cell
What does intercellular mean
The communication or substances between cells
What does extracellular mean
The communication or substances outside the cell
Define plasmodesmata
Microscopic channels which traverse the cell walls of plant cells and some algal cells, enabling transport and communication between them
What is the first grouping which plant tissue can be divided into
Meristematic tissue and permanent tissue
What is meristematic tissue
Undifferentiated and unspecialised tissue which have no specific function in the plant yet except growth. It contains actively dividing cells (undergo mitosis) that result in the formation of other tissue types
Where is meristematic tissue found
In the growth regions of the plant - tips of the stems and root, axillary buds etc.
What groups can meristematic tissue be divided into
Apical Meristem (primary growth) Lateral Meristem (secondary growth)
What are the characteristics of meristematic cells
- Relatively small
- Cubic in shape
- No vacuole present
- Large and noticeable nucleus
- Cell walls are thin
- Dense cytoplasm
- Densely packed and have no intercellular spaces
What is the apical meristem responsible for
The primary growth of the plant
Where is are the apical meristem cells found
At the points of roots and stems
Fill in the missing word
Through _____ the apical meristem cells are responsible for _______ growth of the plant
Through mitosis the apical meristem cells are responsible for the longitudinal growth of the plant
What is another word for the lateral meristem
the cambium
What is the lateral meristem responsible for
the secondary growth of the plant
Where can the lateral meristem cells be found
Between the Xylem and Phloem in the vascular bundles of dicotyledonous plants
What does the lateral meristem do also comment on their structure in the plant
The cells increase the girth of the plant, meaning the plant will grow thicker. The basic structure of these cells are the same as the apical meristem tissue but some of the cells are flatter and slightly elongated and some might have a thicker wall
What is permanent tissue
tissue that already differentiated to perform a particular function
What can permanent tissue be divided into
- Simple tissue
it consists of only one cell type
(Ground and Dermal tissue) - Complex tissue
tissue consisting of more than one type of cell
(Vascular tissue)
What groups does ground tissue consist of
Parenchyma. Collenchyma and Sclerenchyma
What groups does dermal tissue consist of
Epidermis and Periderm
What is the most general and abundant of ground tissue
Parenchyma
What are the functions of parenchyma cells
- Photosynthesis
done by the chlorenchyma which is parenchyma containing chloroplasts, it occurs in green plants especially the mesophyll of leaves - Storage
of food such as starch and oils. Vacuoles store salts an sugar in the plant. Occurs in colourless plant parts, especially the marrow, but also in the cortex, seed lobes and endosperm of seeds - Secretion
can secrete tannins, resin, hormones, enzymes and nectar - Meristematic functions
These cells can differentiate into other types of cells, allows growth - Filling tissue
these cells are found as filling tissue in plant organs - Gas exchange
done by the aerenchyma which contains large open spaces. In aquatic plants this helps with floating
Describe the cell structure of parenchyma
- Large vacuoles
- Large cells with thin cell walls
- Some can contain chloroplasts
- Contains intercellular spaces
- Round to elongated in shape
What is collenchyma
simple, permanent tissue typically found in the shoots and leaves of herbaceous plants
What are the functions of collenchyma cells
- To lend support for the plant
- Strengthening in the plant structure
- Photosynthesis (but only when the cells contain chloroplasts)
Describe the structure of collenchyma
- Irregular thickened walls, especially in the corners of these cells
- The cells remain alive, even when mature
- Mostly found as strands in ground tissue
What are the types of sclerenchyma and define them
Sclereids: They have thickened, highly lignified walls with pits running through the walls. They support the soft tissues of pears and guavas and are found in the shells of some nuts.
Fibres: They are long and arrow and have thick lignified cell walls. They provide mechanical strength to the plant and allow for the conduction of water. They occur in groups in wood, the inner part of the bark and as vascular tissue
What fabrics are sclerenchyma tissues important components of
flax, jute and hemp. Fibres are important components of ropes and matrasses because of their ability to withstand high loads. Fibres found in jute are useful in processing textiles, given that their principal cell wall component is cellulose
What are the functions of sclerenchyma cells
- Acts as strengthening tissue
2. Provides mechanical support for the plants
Describe the cell structure of sclerenchyma
- Cell walls are uniformly thickened with lignin
- Each cell contains small lumen
- Has no living content in its mature form, in reality the cells are dead
- Cell walls are not as elastic as the walls of parenchyma and collenchyma
Describe the epidermis
A single layer of cells that covers plant leaves, flowers, roots and stems. It is the outermost cell layer of the plant body and plays a protective role in the plant.
Herbaceous plants are covered by an epidermis that has one layer of cells.
Initially woody plants also have an epidermis, but as organs, especially the stems and roots, grow thicker, the epidermis tears and is replaced by the periderm. The periderm in older woody plants forms the bark
List 7 points on the structure of dermal tissue and the functions of those structures
Structure
1. Layer of cells covering the surface of the entire plant
(This acts as a barrier to fungi and other micro organisms and pathogens)
- Layer is thin and transparent
(Allow for light to pass through, thereby allowing for photosynthesis in the tissues below) - Epidermal tissues have abundant trichomes which are tiny hairs projecting from the surface of epidermis. Trichomes are abundant in some plant leaves
(Leaf trichomes trap water in the area above the stomata and prevent water loss) - Root hairs are elongations of epidermal cells in the root
(Root hairs maximise the surface area over which absorption of water from the soil can occur) - Epidermal tissues in leaves are covered with a waxy cuticle
(The waxy outer layer on the epidermis prevents water loss from thee leaves) - Epidermal tissues contain guard cells containing chloroplasts
(Guard cells control the opening and closing of the pores known as stomata thus controlling water loss in plants) - Some plant epidermal cells can secrete poisonous or bad tasting substances
(the bitter taste of the substances deter browsing and grazing by animals)
What is a stoma
a pore found in the leaf and stem epidermis that allows for gaseous exchange. It is bordered on either side by a pair of specialised cells known as guard cells
What are guard cells
bean shaped specialised epidermal cells, found mainly on the lower surface of leaves, which are responsible for regulating the size of the stomata opening
What is stomata
The stoma and guard cells together
What does stomata do
the stomata in the epidermis allow oxygen, carbon dioxide and water vapour to enter and leave the leaf
True or false
Guard cells contain chloroplasts and can participate in photosynthesis
true
Explain how guard cells work
Opening and closing of the guard cells is determined by the turgor pressure of the two guard cells.
The turgor pressure is controlled by movements of large quantities of ions and sugar into the guard cells.
When guard cells take up these solutes, the water potential decreases causing water to flow into the guard cells via osmosis.
This leads to an increase in the swelling of the guard cells and the stomatal pores open.
What are the functions of the epidermis
- To protect the other plant tissues against harm and from drying out
- Cuticle will prevent excessive water loss
- Absorption of water and minerals, done by root hairs
- Gas exchange, controlled by guard cells
- Allows photosynthesis- by being transparent, sunlight can reach the deeper tissue layers
What is a type of complex tissue
Vascular tissue, the Xylem and Phloem are the vascular tissues found in plants
What does vascular tissue in plants do
They form the transport system within the plants and have vein like structure and arrangement
What does Xylem consist of
It consists mainly of wood vessel segments and tracheids
Does xylem contain living content
xylem does not contain any living contents
What cell types can Xylem consist of
- Tracheids
- Wood vessel segments (tracheids and wood vessel segments are responsible for transport)
- Parenchyma (responsible for the storage of the substances)
- Fibres (play an important role in support and strengthening)
What are the functions of Xylem
- Upwards transport of water and dissolved mineral salts, from the roots to the leaves. Wood vessels are the most important cells responsible for water transport
- Strengthening and support in woody plants, form wood
- Transport will only take place in one direction
Describe wood vessel segments
- Have thickened cell walls
- No living cell contents
- They have elongated cells that make a long tube because the cells are arranged end to end, and the point of contact between the two cells is dissolved away
- Round in cross section
- Pits for lateral transport
- Have lignin in their secondary wall, which provides additional strength and support. The lignin can form spiral, net or ring patterns
- Transverse walls are perforated
- Hollow, continuous tubes. (they are hollow because they lack protoplasm)
Describe tracheids
- They have elongated cells with pointed ends
- Tracheids do not have end openings like xylem vessels
- The ends overlap with one another, with pairs of pits present which allow water to pass through horizontally from cell to cell
- They have thickened cell walls containing lignin
What does the phloem consist of
It consists of living cells
True or false
The phloem does not have thickened walls
true
What are the phloem system’s two main cell types
sieve tubes and companion cells
What are the 4 cell types that help with phloem system transport
- Sieve tubes
- Companion cells (sieve tubes and companion cells responsible for transport of nutrients)
- Parenchyma (responsible for the storage of substances
- Phloem fibres (responsible for support and strengthening)
What are the functions of phloem
- The transport of dissolved organic food from the leaves to other plant parts
- The sieve tubes are the main transport for cells
Describe sieve tube elements
- Rounded in the cross sections
- Elongated cells
- Transverse wall between the connecting segments are perforated and known as sieve plates
- Can have thin to slightly thickened walls
- Pits and plasmodesmata occur
- Closely associated with companion cells
- Mature sieve cells do not contain a nucleus but are metabolically active
Describe companion cells
- Thin walls
- Large nucleus
- Closely associated with sieve tubes
- Nucleus is responsible for the metabolic activity of both companion cells and sieve tube cells
- Contains pits and plasmodesmata
