Plants Flashcards
Function of Leaf
Contains chlorophyll to carry out photosynthesis
Function of Stem
Support
Contain vessels for transport
Apical & Lateral Growth
Function of Flower
Reproduction
Function of Root
Anchorage
Absorption
Storage
What are the two types of meristem
Apical (vertical) meristem
Lateral (horizontal) meristem
Apical Meristem
Primary growth - lengthening of plant
Occurs at tips of shoots and roots
Produces new leaves & flowers
Lateral Meristem
Secondary growth - widening of plant
Occurs at the cambium
Produces bark on trees
What are the different things in a cross-section of a leaf (listed top to bottom)
Waxy Cuticle Upper Epidermis Palisade Mesophyll Spongy Mesophyll Air Space Vascular Bundle (contains Xylem & Phloem) Guard Cells Stoma Lower Epidermis
Function of Waxy Cuticle
Barrier - stops water evaporating from the cells
Function of Upper Epidermis
Prevents water loss by evaporation.
Any damage to the outer layer won’t damage photosynthesising cells
No chloroplasts - light passes through easily
Function of Palisade Mesophyll
Near the top of the leaf - absorbs maximum light for photosynthesis
Many chloroplasts - 80% of photosynthesis happens here
Most chloroplasts are at the top of cells
Box-like arrangement of palisade - tightly packed - maximise photosynthesis
Function of Spongy Mesophyll
Increases SA for CO2 absorption by cells.
Allows diffusion of gases in & out of cells
Irregular shaped cells - many air spaces - lets CO2 move towards Palisade Layer for photosynthesis. Also provides big SA - gas exchange
Still contain some chloroplasts so photosynthesis can still occur
Function of Vascular Bundle
Transports substances around the plant (contains xylem and phloem)
Function of Lower Epidermis
Contain guard cells that open and close the stomata (pores) to allow CO2 to diffuse in or to let Oxygen out. Also controls Water Loss.
Xylem Cells
Elongated, dead cells arranged end to end to form continuous vessels (tubes)
No cytoplasm
Tough walls containing a woody material calledLignin - builds up in spirals in cell walls - can withstand pressure from the water + provide support to plant stem.
The contents & end walls break down to form a hollow centre (Lumen)
Involved in a process that carries water & mineral ions from the roots to the leaves, called the transpiration stream.
Xylem cells are alive when first formed but after Lignin forms they die and form long hollow tubes.
Xylem vessels form the wood in a tree.
Where is the Vascular Bundle containing the Xylem found in the Roots
Centre of Root because it is strong and can resist forces that could pull the plant out of the ground.
The Vascular Bundle looks like a circle & there is a smaller ring inside that where there is a plus-like structure which is the Xylem and the bit in the gaps is the Phloem
Where is the Vascular Bundle containing the Xylem found in the Stem
Near the edge to resist compression and bending forces caused by the plant’s weight and the wind.
The Vascular Bundle looks like a circle again with a smaller ring inside it but now there are multiple oval-structures that overlap this smaller ring. The part of the oval that is on the inside of this ring is the Xylem and the outside part is the Phloem.
Where is the Vascular Bundle containing the Xylem found in the Leaf
In Spongy Mesophyll layer.
The Vascular Bundle looks like a circle again but inside is different. The Xylem occupy the top half of the circle while the Phloem take the bottom half of the Vascular Bundle.
Transpiration stream
The flow of water through a plant, from the roots to the leaves, via the xylem vessels. Water will eventually be lost by evaporation out of the stomata
Transpiration
The loss of water from leaves by evaporation through the stomata
How does the Transpiration Stream work
Water moves thru plant from roots - leaves via xylem
When guard cells are open, water evaporates out of leaf via stomata
Shortage of water - water drawn up from roots via Xylem to replace it
Water molecules in Xylem - strongly attracted to each other - slight electrical charge - cohesion - links up all the water molecules - hydrogen bonding - continuous column of water pulled up stem.
More water is drawn into the roots via osmosis to replace water lost inside the roots
Repeat
Why is transpiration important
Cooling of the plant Mineral transport Getting water to cells - water is a reactant in Photosynthesis - osmosis, enabling turgidity & support
What are the 4 Factors that can change the rate of transpiration
Light - Bright Light Increases
Temperature - Faster in Higher Temperatures
Wind - Faster in Windy Conditions
Humidity - Slower in Humid Conditions
Why is Light a factor that can change the rate of transpiration
The stomata open wider to allow more CO2 into leaf for Photosynthesis (when they open wider more water can escape)
Why is Temperature a factor that can change the rate of transpiration
Evaporation & Diffusion - faster at higher Temperatures (more thermal energy)
Why is Wind a factor that can change the rate of transpiration
Water Vapour removed quickly by air movement, speeding up diffusion of more Water Vapour out of the leaf (concentration gradient remains steep)
Why is Humidity a factor that can change the rate of transpiration
Diffusion of Water Vapour out of the leaf slows down if the leaf is already surrounded by moist air (concentration gradient is closer to equilibrium)
Why is water uptake rate not the same as transpiration rate?
Only a rough gauge. Some water taken up by the roots is used in photosynthesis (5-10%).
Transpiration will still occur in a water shortage, which will ultimately lead to wilting
What does Potometer measure
Water Uptake (you could use this to estimate the transpiration rate if you assume water uptake is directly linked to water loss.
How does a Potometer work
During transpiration water evaporates from leaves and so more water will enter to replace it.
We can use this to measure water uptake or ESTIMATE transpiration rate.
The potometer is filled with water and all air bubbles are removed using a pipette.
A shoot of a plant is cut underwater to ensure it’s water-filled and prevents air locks.
The shoot is inserted into the rubber tubing at the end of the potometer.
The potometer is raised above the water so that a bubble of air is taken up.
The potometer is lowered into the water. The distance travelled by the air bubble is recorded over a period of time.
This distance can be divided by how long it took to travel that distance to work out the Water Uptake.
Guard Cells
Guard cells open and close to control gas exchange and water loss out of the stomata.
How is a Guard Cell adapted to perform its task
Inner cell wall is thicker to cause the cell to curve to make a hole.
How do Stomata open
In bright light (need more carbon dioxide for photosynthesis):
Potassium ions move into the guard cells
This makes the guard cells more concentrated (less dilute) than surrounding tissue
Water moves into the guard cell by osmosis (across a partially permeable membrane)
Cell swells unevenly because the thicker inner cell wall is less flexible than the thinner outer wall
How do Stomata close
In low light the guard cells lose water and become flaccid so they stop swelling and close.
Why are there more stomata on the bottom surface of a leaf than the top surface
Fewer / no stomata on top surface of leaf - in direct sunlight - transpiration rate - high - water loss - evaporation of water vapour. Concentration gradient - steep. Plant - wilt & possibly die.
(Most) plants have evolved to have stomata only on the lower surface - CO2 can still move in & out of the stomata - but less water is likely to be lost via transpiration
The plant is less likely to wilt due to excessive water loss
Function of Stomata
Gas Diffusion (CO2 in, Oxygen out) & Control of Water Loss
Function of Phloem
Translocation - movement of dissolved sugars and amino acids around the plant
[Chemicals e.g. pesticides will also move through the phloem by translocation]
Why is Translocation important
Sugar made in the leaves via photosynthesis (source) & needs to move location to be used for either respiration or storage (sink)
How does Translocation work
Sucrose at source (leaf) (in Summer) - actively pumped into phloem by companion cell as it has a lot of mitochondria.
Water follows by osmosis - huge internal pressure. (10x more than in a tyre).
This forces the dissolved sugar solution to move through sieve plates.
Sink (roots) (in Summer) constantly using sugar - lower pressure.
Moves from higher pressure to lower pressure.
What is a Source & Sink
Source - where substances are made
Sinks - where substances are used or stored
Where is the Source & Sink located in Spring (growth period)
Source - Storage organs (e.g. roots)
Sink - Growing areas (e.g. new shoots & stem)
Where is the Source & Sink located in Summer
Source - Photosynthesising leaves
Sink - Roots for storage of excess sucrose (stored mostly as starch) (for Winter)
Where is the Source & Sink located in Winter (no leaves so no photosynthesis)
Source - Storage organs (no other source of sugar)
Sink - Other parts of plant for respiration
Structure of Phloem
Found in the vascular bundle
Unlike xylem - made of living cells lined end to end [Xylem are made of dead cells due to lack of cytoplasm]
Vessels contain cytoplasm
Phloem Cell Adaptions
Phloem vessels are made of phloem cells aligned in a column (can transport up & down easily)
The cell walls between phloem cells break down - form sieve plates. These plates have holes in them (perforated) - allow water carrying dissolved food to move freely along the tubes
Companion cells containing a nucleus & lots of mitochondria surround phloem vessels. The mitochondria of the companion cells transfer the energy needed for translocation to occur.
Have lost most of their internal structure (e.g. no vacuole or nucleus and limited amount of cytoplasm) - helps reduce any resistance during translocation.
Two-way flow - allows substances to be transported all around the plant
What is the Scientific name of the Marram Grass Leaf
Ammophila arenaria
Xerophyte
A plant adapted to live in dry conditions
Marram Grass Leaf Adaptions
Reduced # of stomata - Less evaporation of water vapour from the leaf
Stomata in sunken pits/grooves - Prevents evaporation of water vapour from the leaf
Stomata surrounded by hairs - Traps water vapour increasing humidity, reduces water vapour gradient
Stomata close - Less evaporation of water
Widespread roots - During rainfall / Condensation allows max absorption of water
High salt concentration found in root cells - Water moves in down a concentration gradient by osmosis
Long tap root - Can reach deep water sources
Few air spaces - Traps water vapour increasing humidity, reduces water vapour gradient
Reduced leaf size - Reduces leaf surface area
Rolled leaf - Reduces leaf surface area
Thicker waxy cuticle - Prevents evaporation of water
Photosynthesis Symbol Equation
6CO₂ + 6H₂O —> C₆H₁₂O₆ + 6O₂
Photosynthesis Word Equation
Carbon Dioxide + Water —> (through Light and Chlorophyll) Glucose (Energy) + Oxygen
How are leaves adapted to maximise Photosynthesis
Large SA - To absorb more light
Thin - Short distance for carbon dioxide to diffuse into leaf cells
Chlorophyll - Absorbs sunlight to transfer energy into chemicals
Network of Veins - To support the leaf and transport water and carbohydrates
Stomata - Allow carbon dioxide to diffuse into the leaf
How is the structure of leaves adapted to maximise Photosynthesis
Epidermis is thin & transparent - To allow more light to reach the palisade cells
Thin cuticle made of wax - To protect the leaf without blocking out light
Palisade cell layer at top of leaf - To absorb more light
Spongy layer - Air spaces allow carbon dioxide to diffuse through the leaf, and increase the surface area
Palisade cells contain many chloroplasts - To absorb all the available light
What is an organism called if it uses light energy to produce its own food
Photoautotroph
(Photo relating to light)
(Autotroph meaning an organism that makes its own food)
Repeatability
checking you can recreate your own results - a way for researchers to verify that their own results are true and are not just chance artefacts
Reproducibility
checking results in a paper can be attained by a different research team, using the same methods - results obtained are not artefacts of the unique setup in one research lab only, reinforces findings and protects against rare cases of fraud
What are the 4 factors that can change the rate of Photosynthesis
Light
Temperature
CO₂ Concentration
Number of Chlorophyll
What is a limiting factor
if we increase that factor, the thing it’s affecting will increase and vice versa for when you decrease that factor.
(e.g. light is a limiting factor in Photosynthesis when the more light you give a plant, the faster Photosynthesis will occur UP TO A POINT. After this point light is no longer a limiting factor, it has plateaued, how much you increase it won’t speed up rate of Photosynthesis anymore. Now something like CO₂ Concentration may be the limiting factor.)
What is not a limiting factor in Photosynthesis
Temperature - The more Temperature there is the more Kinetic Energy there is which means a faster reaction. There is a PEAK but after you exceed that OPTIMUM Temperature which is the max rate of Photosynthesis, the more temperature you give, the slower Photosynthesis occurs as after it’s reached its peak, Enzymes will DENATURE and vibrate too much then break shape.
Intensity Equation
1/d² where ‘d’ is the distance between the light source and the object affected.
