Histology Flashcards
What is Histology?
The study of tissues
What is the importance of tissues
Increase the efficiency of an organism by division of work
What are the characteristics of cells in a tissue?
- Generally share a similar origin in the embryo
- They may be of same type or of different type
- Share a similar function
- They are physically linked
What is an organ?
A number of tissues working together as a functional unit
What is a system?
A functional unit of organs
List plant tissues
- Parenchyma
- Collenchyma
- Schlerenchyma
- Xylem
- Phloem
List animal tissues
- Epithelial tissues
- Connective tissues
- Muscle tissues
- Nervous tissues
What is the most common characteristic of all parenchyma?
They are living tissues
Describe the structure of parenchyma
- The cells are living
- The cells are roughly spherical or elongated
- The cells have thin cellulose cell walls
- The cells have a large central vacuole
- The cytoplasm and nucleus of the cells are peripheral
- Made up of tightly packed cells
- The cells have large intercellular spaces
- It is made up of one type of cell
Give the functions of parenchyma
-Provide support to the plant
-Gaseous exchange
-Store food
-Exchange materials eg water, oxygen, carbon dioxide etc
-Allow growth of the plant
-Passage of water and mineral salts
Give the adaptations of the parenchyma to its function
- The cells have thin, permeable cell walls that allow exchange of mater eg water, mineral salts, glucose, oxygen and carbon dioxide etc
- The cells are closely packed giving them mechanical strength which provides support to the plant
- The cells have a concentrated central vacuole which is osmotically active thus providing support via turgidity in herbaceous plants
- The large central vacuole of the cells provides adequate space for food storage in the plant
- The cells have numerous large intercellular spaces making it suitable for gaseous exchange
- The parenchyma is made up of unspecialized cells thus it can perform a variety of functions
- Parenchyma is made up of living cells which allows growth
- The parenchyma are tightly packed which enables them to act as packing tissue in plants
Where is parenchyma tissue found?
- Rays in woods
- Cortex
- Packing tissue in xylem and phloem
- Pith
Describe the structure of the epidermis
- One cell thick
- Living
- Cells are elongated
- Cells are flattened
- Tightly packed cells
- Transparent
- Has a waxy cuticle; a waterproof layer of cutin
What are the functions of the epidermis as a modified parenchyma?
- Protection of the plant from desiccation and infection
- Allow light to reach the palisade cells for photosynthesis
What name is given to the layer of cells that replaces the epidermis when it wears out?
Cork layer/ cork cells
Describe the structure of the guard cells
- Have pores called stoma
- Contain chloroplasts
- Occur in pairs
- Each cell is bean shaped
- Inner layer is thicker than outer layer
What are the functions of the guard cells as modified parenchyma?
- Control the opening and closing of the stomata
- Allow gaseous exchange
- Control transpiration
- Site for photosynthesis
Where are guard cells found?
- Leaf epidermis
- Stems especially herbaceous
Describe the structure of hair like extensions
- Unicellular or multicellular
- May be hooked
What are the functions of the hair like extensions as modified parenchyma?
- Aid in seed dispersal
- Absorb water and mineral salts for plants
- Reduce water loss
- Protection
- Promote cross pollination
- Feeding in carnivorous plants
Where are hair like extensions found?
- Roots
- Climbing plants
Describe the structure of the glandular cells
- May be hair like
- Have glands
What are the functions of the glandular cells as a modified parenchyma?
- Secretion of sticky substances
- Secrete enzymes for digestion and absorption of food in insectivorous plants
Where are glandular cells found?
- Insectivorous/ carnivorous plants
Describe the general structure of the mesophyll cells
- Roughly spherical or irregular
- Two layers (palisade above and spongy below)
Describe the structure of the palisade mesophyll
- Numerous chloroplasts
- Tightly packed
- Regularly shaped
What is the function of the palisade layer in plants?
- Stores starch
- Mechanical support
Describe the structure of the spongy mesophyll
- Many intercellular spaces
- Irregularly shaped cells
- Few chloroplasts
What is the function of the spongy layer in plant leaves?
- Sites for gaseous exchange
Describe the structure of chlorenchyma
- Living
- Contain numerous chloroplasts
What are the functions of the chlorenchyma?
- Carry out photosynthesis
Where are chlorenchyma found?
- Palisade mesophyll
- Outer regions of the cortex
Describe the structure of the endodermis
- Living
- May be elongated and flattened
What are the functions of the endodermis?
- Selective barrier to the movement of water and mineral salts between the cortex and xylem in roots
- Responsible for geotropic responses in roots
- Store starch grains
- Suberin maintains one-way flow of water from the roots to the stem
Where is the endodermis found?
- Most conspicuously in roots
- Innermost layer of the cortex
Describe the structure of the pericycle
- Living
What are the functions of the pericycle?
- Produces lateral roots
- Contributes to secondary growth
Where is the pericycle found?
- Only in roots
Describe the structure of companion cells
- Living
- Have numerous mitochondria
- Living
- Elongated and narrow
- Small vacuoles
- Dense cytoplasm
- Adjacent to sieve tubes
What are the functions of the companion cells?
- Load food into the phloem
Where are companion cells found?
- Adjacent to sieve tubes
Describe the structure of collenchyma
- Living
- Cell walls are unevenly thickened with cellulose
- End walls tapper
- Elongated cells
- Polygonal shaped cells
- Tightly packed cells
- Large central cell vacuoles
What are the functions of the collenchyma cells?
- Provides mechanical support
Where are collenchyma cells found?
- Outer regions of the cortex
- Young plants (herbaceous)
Describe the structure of sclerenchyma
- Mature cells are dead
- Empty lumen
- Lignified
- Uniformly thickened walls
- Interlocking cells
- Consist of fibres and sclereids
Describe the structure of fibres as sclerenchyma
- Elongated
- Lignified
- Have pits
- Tapering interlocking cells
- Polygonal shaped
- Form strands
Describe the structure of sclereids
- Roughly spherical
- Narrow lumen
What are the functions of the sclerenchyma?
- Support
Describe the structure of xylem
- Made up of parenchyma, tracheids, vessels, fibres
- Elongated cells
- Cells are joined end to end
- Cells are dead
- Tubes are hollow/ tubular
- Lignified
- Bordered pits
- Narrow lumen
State the functions of xylem
- Conduct water and mineral salts
- Provide support
What is the use of a torus in conifers?
- Controls entry and exit of water between the cells
Describe the structure of tracheids
- Arranged in rows with overlapping ends
- Elongated cells
- Empty lumen
- Cells are dead
- Tubes are hollow/ tubular
- Lignified
- Bordered pits
- Narrow lumen
Describe the structure of vessels
- Long and tubular
- Empty lumen
- Lignified
- Perforated
- End walls are broken down
- Cylindrical shape
Describe the structure of fibres
(sclerenchyma)
- Shorter
- Narrow
- Thicker walls
- Pits
- Overlapping end walls
- Dead
Describe the structure of phloem
- Living cells
- Elongated
- Tubular
SIEVE TUBES
- Narrow
- Have strands of cytoplasm
- Mature sieve tubes lack a nucleus
- Elongated
- Sieve pores at their end walls
- Have sieve plates
COMPANION CELLS
- Dense cytoplasm
- Thin cellulose cell walls
- Metabolically active
- Numerous mitochondria
- Small vacuoles
- Elongated
- Narrow
- Adjacent to sieve tubes
- Numerous plasmodesmata
State the functions of phloem
- Transport of food throughout the plant
Give the similarities between the xylem and phloem
- Both are conducting tissue
- Both are elongated
- Both exist as parenchyma
- Both are perforated
- Both exist as fibres
- Both are tubular
Give the differences between xylem and phloem
XYLEM
- Conducts water and mineral salts
- Consist of mostly lignified
- Movement is from the roots upwards to the rest of the plant
- Cells are dead when mature
- Does not require energy to transport materials
PHLOEM
- Transports organic material
- Cells are not lignified
- Movement is from the leaves throughout the plant
- Cells are alive when mature
- Requires energy to transport materials
What are meristematic tissues?
Group of cells that retain the ability to divide by mitosis
Where are meristematic tissues located?
Apical growing points of plants