Plant Tissues, Organs And Systems Flashcards
What are the main parts of a leaf?
- waxy cuticle
- upper epidermis
- palisade mesophyll
- spongy mesophyll
- (vascula bundle)
- lower epidermis
- (guard cells and stomata)
What is the waxy cuticle?
Top layer of a leaf
- waterproofs leaf and stops water evaporating out of top
What is the palisade mesophyll?
Second layer of leaf cells
- Regular box-like structure to maximise photosynthesis
- Main site of photosynthesis, ~80% of chloroplasts found here
- chloroplasts near top of cell where there is more light to maximise photosynthesis
What is the upper epidermis?
Top layer of leaf cells
- protective barrier against damage and pathogens
- translucent to let light through to palisade mesophyll for photosynthesis
What is the spongy mesophyll?
Third layer of leaf cells
- less tightly packed, irregular shaped cells
- ~20% chloroplasts found here
- air spaces for gas exchange
What is the vascula bundle?
Located in the spongy mesophyll
- contains xylem and phloem
- used for transport
What is the lower epidermis?
Bottom layer of lead cells
- protective layer
- has guard cells
What is the xylem?
- Elongated dead cells, arranged end to end to form continuous vessels
- No cytoplasm
- Have tough walls containing a woody material called LIGNIN (iykyk)
- hollow centre called LUMEN
What does lignin do in the xylem
Builds up in spirals in cell walls. These spirals are very strong to withstand water pressure and provide support
What is the transpiration stream?
The stream of the xylem that carries water and mineral ions one way from the roots to the leaves
What does the vascula bundle look like in leaf, stem and root
Leaf the top is circles of xylem and bottom is circles of phloem
Stem there is a ring of cartoon pills around the edge with the phloem being the outer bit and the xylem being the inner
In the roots there is a ‘+’ of xylem, and circles of phloem surrounding
What is the phloem?
- made up of living cells lined end to end
- vessels contain cytoplasm, but limited amounts to reduce resistance of flow
-no nucleus or vacuole - transport sucrose and amino acids in the translocation stream
- this goes both ways between leaves (source) and roots (sinks)
- have companion cells found along outside of phloem vessel with Nuclei and lots of mitochondria to provide energy for translocation
- have perforated sieve plates to allow movement of substances through phloem vessel
What is the translocation stream?
The movement of sucrose and amino acids between leaves and roots and vice versa via the phloem.
How do guard cells work?
- In bright light, more CO2 needed for photosynthesis
- inner cell wall thixker than outer to cause cell to make a hole
- potassium ions move into guard cells via active transport
- makes guard cells more concentrated/less dilute than surrounding tissue
- water moves into cell via Osmosis
- cell swells unevenly as thicker cell wall less flexible than thinner outer wall
- opens stomata I guess??
What adaptations do guard cells have for their purpose?
-Thicker inner wall than outer wall
-Lots of mitochondria for active transport
