plant tissues, organs and systems Flashcards
what are the 3 types of meristem and where are they found
- roots (root apical meristem)
- sides around vascular tissue in stems (lateral meristem)
- ## tips (shoot apical meristem)
what are plant growth tissues?
meristems - groups of pluripotent unspecialized cells
name layers of internal structure of a leaf in order (7)
- waxy cuticle layer
- upper epidermis
- palisade cells (palisade mesophyll layer)
- vascular bundle (phloem and xylem)
- spongy mesophyll with air spaces
- lower epidermis
- guard cells and stomata
what is the structure and function of the cuticle layer?
waxy - helps reduce water loss from evaporation
what is the structure and function of the upper epidermis?
no chloroplasts, thin trasparent cells - lets light through to mesophyl
what is the structure and function of the palisade cells?
many chloroplasts mostly at the top of the cell so they recieve the most light , large surface area - 80% of photosythesis happens here
what is the structure and function of the mesophyll cells?
(in the spongy mesophyll tissue)
irregularly shaped so there is space for air to allow gases to diffuse in and out of the cells
what is the structure and function of guard cells
banana shaped cells, come in pairs, can open and close - control the exchange of gases and water loss
what are some types of plant tissues? (5)
- epidermal tissue (covers whole plant)
- palisade mesophyll tissue
- spongy mesophyll tissue
- meristem tissue
- xylem and phloem (vascular tissue)
plant organs
role of leaf
- site of photosynthesis
- site of water loss by transpiration
- site of gas exchange
plant organs
role of stem
- gives plant structure/support
- containx xylem and phloem for structure
- can photosynthesize
- tranpiration stream
plant organs
role of roots
- anchors plant
- absporbs water and dissolved minerals
what 2 types of cell make up a plant’s vascular tissue?
- xylem
- phloem
what do phloem transport?
dissolved sugars from leaves to the rest of the plant through translocation
what do xylem transport?
water and minerals from roots to the leaves through the transpiration stream
what is transpiration?
the movement and loss of water in plants, the evaporation of water vapour from the stomata of a leaf
how are xylem cells adapted for transpiration?
- dead (no cell contents)
- hollow which means there is lots of space for the transpiration stream
- joined end to end with no end walls for a continuous stream of water
- strenghtened by lignin
what is used to measure rate of traspiration?
potometer - as water is transpired water levels go down/ air bubble moves along
how does water (and minerals) move through a plant through transpiration? (8)
- root cells have lots of mitochondria and large surface area for rapid active transport of mineral ions
- water enters root hair cells and moves along roots one cell at a time through osmosis
- enters the xylem, and moves up the stem
- enters and moves through leaf through osmosis
- in the leaf, some water is used for photosynthesis
- the remaining water evaporates into air spaces in the spongy mesophyll, making the humidity high
- water is evaporated through the stomata creating a shortage of water so more water is draw up through xylem vessels to replace it
- this makes the cycle repeat, creating a continous transpiration stream of water through the plant
in what direction do xylem transport water and minerals?
upwards only (roots to shoots)
how do stoma open/ close?
stoma open when
-guard cells fill with water (turgid) from osmosis
- thick inner wall doesn’t stretch as much as thinner outer wall so it bends (banana shape) which means it opens
how are guard cells adapted to reduce water loss?
- when plant needs more water, guard cells become flaccid and stomata close
- sensitive to light + close at night > water not needed for photosynthesis so doesn’t need to be lost
- more stomata on undersides of leaves > lower side is more shaded and cooler so less water evaporates and is lost
what factors affect the rate of transpiration? (4)
- light intensity (brighter = faster rate)
- temp (warmer = faster)
- air flow (better = faster)
- humidity (drier = faster)
why does rate of transpiration increase as light intensity increases?
- stomata close in the dark since they don’t need to let CO2 in for photosynthesis
- when stomata are closed, little water can escape
why does rate of transpiration increase as air flow gets better (stronger wind)?
strong wind > water vapour outside the leaf is blown away > mantains steep concentration gradient > diffusion of water vapour from stomata to outside happens faster
why does rate of transpiration increase as temp increases?
water particles have more energy to evaporate and diffuse out of the stomata
why does rate of transpiration increase as humidity decreases (air gets drier) ?
if air is dry but air in the spongy mesophyll/ lower epidermis is humid there is a higher concentration gradient > faster rate of diffusion
how do different plants control water loss (4) ?
- thickness of waxy cuticle
- number of stomata on underside to protect from environmental factors
- needle-like, rolled up or spiny leaves
- stomata in pits on leaf surface
what are the parts of a phloem vessel? (2)
- phloem cells
- companion cells
(‘sink’ and ‘source’ cells)
how are phloem vessels adapted for translocation?
phloem cells
- elongated
- thin walls (short diffusion path)
- contain little cytoplasm, no nucleus
form sieve tubes due to sieve plates between cells
companion cells
- control activities of phloem
what is translocation
movement of sugars (and amino acids) in plants
describe translocation (5 steps)
(remember source to sink)
- sugars made in leaf cells by photosynthesis (source)
- sucrose actively moved into the companion cell from the leaf
- from companion cell, diffuse into phloem vessel
- the high concentration of sugar at the top of the phloem vessels causes water to enter through osmosis
- movement of water into phloem vessel causes translocation of sugars to the root (sink) where they leave the vessel and are stored as starch
in what direction does translocation happen?
**BOTH **
- upwards > root (sink) to leaves (source)
- downwards > leaves to root
what is transported through translocation?
- carbohydrates and starch as SUGARS
- protiens as AMINO ACIDS
(would be too large to pass through cell membranes)
