Week 5 - Evolution and diversity of plants 2

Question 1

What are the key traits of seed plants?

Answer 1

Sporophyte embryo + endosperm + seed coat

Question 2

What are advantages of seeds ?

Answer 2

Protection of embryo

Nourishment during development

Dispersal across environments

Dormancy allows survival through unfavourable conditions

Question 3

What are the 4 groups of gymnosperms?

Answer 3

Conifers = needle leaves
Cycads = palm-like
Ginkgo = fan-shaped leaves
Gnetophytes = flower-like

Question 4

What are some gymnosperm innovations?

Answer 4

• Secondary growth via vascular cambium - the increase in thickness or girth of plant stems and roots
• Non-motile sperm
• Independent fertilization from water
• Vascular anatomy : tracheids, protostele to eustele evolution
• Complex monopodial branching

Question 5

What are some Angiosperm evolutionary innovations ?

Answer 5

• Flowers = efficient sexual structures, attract specific pollinators
• Double fertilization
• Fruits = aid in dispersal and protects seeds
• self-incompatibility = maintain genetic diversity

Question 6

What is the function of sepals?

Answer 6

Protection

Question 7

What are the functions of petals?

Answer 7

Attraction

Question 8

What are the flowers reproductive organs?

Answer 8

Stamens = male
Carpels = female

Question 9

What are inflorescences ?

Answer 9

Clusters of flowers on a branch

Question 10

How do flowers avoid self-pollination?

Answer 10

Dichogamy = different maturation times
Herkogamy = Structural separations
Dicliny = separate male/female flowers
Self-incompatibility = Genetic rejection of self-pollen

Question 11

What is the meristem and what does it contain?

Answer 11

A structure at the apex
of the plant that contains the stem cells
which are the undifferentiated cells that
produce all plant organs.

Question 12

What is a lateral meristem called?

Answer 12

Vascular cambium- is a type of lateral meristem, a ring of stem cells that lies between the xylem and phloem in the stem/root. Produces a secondary xylem and phloem

Question 13

Where is the vascular cambium located?

Answer 13

In between the xylem and phloem

Question 14

Why is the evolution of non-motile sperm beneficial?

Answer 14

No reliance on water

Question 15

From a cross sections of Pine stem which order would these sections be in, start from the outer edge to the middle: Vascular cambium, Primary phloem, Secondary xylem, Pith, Secondary phloem, primary xylem.

Answer 15

Furthest out:
1. Primary phloem
2. secondary phloem
3. Vascular cambium
4. Secondary xylem
5. Primary xylem
6. Pith
Inside

Question 16

Are Conifers gymnosperms or angiosperms and give can example?

Answer 16

Gymnosperms
e.g. pine

Question 17

What is the key example of a lycophyte?

Answer 17

Selaginella

Question 18

There are 2 groups of land plants, bryophytes and …………………….., what is the other group called (contains plants with xylems/tracheids

Answer 18

Tracheophytes

Question 19

Why is it important to understand the selaginella life cycle?

Answer 19

It is like a snapshot of plant evolution that helps explain the critical steps that led to the success of modern seed plants (gymnosperms and angiosperms).

It also helps us understand the transition from water-dependent reproduction (like spores) to land-based, protected reproduction (like seeds).

Question 20

What is the endosperms function in a seed and what did it derive from?

Answer 20

Food storage
The megagametophyte

Question 21

What are the unifying traits of flowering plants?

Answer 21

Have flowers
Have carpels
Double fertilization

Question 22

What is Darwin’s ‘Abominable Mystery’ ?

Answer 22

The problem of the origin of
angiosperms

Question 23

What happens during double fertilization of flowering plants?

Answer 23

First Fertilization: Sperm cell + egg cell → Zygote (2n) → Embryo.

Second Fertilization: Sperm cell + two polar nuclei → Endosperm (3n).

Question 24

How does the transfer of pollen differ between gymnosperms and angiosperms?

Answer 24

In angiosperms pollen doesn’t need to be in contact with the ovule like it does in gymnosperms

Question 25

What does dehiscent or indehiscent mean in terms of fruit types ?

Answer 25

dehiscent = releases seeds indehiscent = doesn't release seeds

Question 26

What does pollinator syndromes mean?

Answer 26

A set of floral traits linked to type of pollination/pollinator

Question 27

To prevent self fertilization where can the pollen be inhibited ?

Answer 27

- At the stigma (no germination) - Style (no elongation) - In ovary (no transfer)

Question 28

What is the perianth?

Answer 28

The term for the Corolla (petals) and Calyx (sepals)

Question 29

What are the 2 largest groups of angiospersm?

Answer 29

Eudicots and monocots

Question 30

How can you distinguish between eudicots and monocots?

Answer 30

Monocots - flower organs in groups of 3 Eudicots - flower organs in groups of 5

Question 31

What are some examples of monocots?

Answer 31

All cereal crops Bamboo ginger

Question 32

What are some examples of eudicots?

Answer 32

Butter cups, cabbages, legumes

Question 33

How do leaf veins differ in monocots vs eudicots?

Answer 33

Monocots - parallel Eudicots - Branching

Question 34

What is one of the most critical limiting factors for plants?

Answer 34

Water

Question 35

What is the stele?

Answer 35

The central part of a plant stem or root, containing vascular tissues (xylem + phloem).

Question 36

What are the 2 hypotheses for why the stele structure evolved?

Answer 36

1. Earlier theory = Says changes in the vascular structure are simply a passive consequence of plants growing bigger and more complex. 2. Later theory = Says the changes in vascular structure were an adaptive solution to drought stress.

Question 37

What doe an embolism mean in a xylem?

Answer 37

Air blockage due to water stress

Question 38

How can embolisms spread?

Answer 38

Tracheids (water conducting cells) are interconnected by pits – small openings through which embolisms can spread

Question 39

What did an increase in the xylem conduits complexity and width lead to ?

Answer 39

Led to taller plants because of the improved efficiencies of water-conducting tissues

Question 40

What cell wall material does vascular plant evolution point to an increase of and why is this beneficial?

Answer 40

Lignified material - for increased structural support

Question 41

What are characteristics of gymnosperm trachieds ?

Answer 41

They are narrow & perforated by complex pit membranes Water passes from cell to cell via pits

Question 42

Angiosperms also have vessels, what are some characteristics of these?

Answer 42

Are wide, short & have open or perforated end walls Water moves via perforation plates

Question 43

Why may vessels be considered to be more efficient than trachieds?

Answer 43

1. Vessels can reach much greater maximum diameters & lengths than tracheids 2. Greater conductivity of vessels reduces the cost of transpiration (carbon trade-off for water)

Question 44

What are the 2 broad morphological types of stomata?

Answer 44

1. Kidney-shaped stoma typical of most species. 2. Dum-bell shaped stoma typical of grasses.

Question 45

What is the function of stomata in tracheophytes ? Where are they found ?

Answer 45

To regulate gas exchange - surface of leaves

Question 46

Where are stomata found in mosses (if present)?

Answer 46

Confined to the solitary spore capsule in the sporophyte.

Question 47

How does it seem plants respond (in terms of stomatal density) to long term changes in CO2 levels?

Answer 47

High CO2 levels = decreasing stomatal density Lower CO2 levels = high stomatal density plants are favoured

Question 48

What two things does xylem structure need to balance ?

Answer 48

Resistance to cavitation against maximum hydraulic conductance

Question 49

What does a high vein density indicate?

Answer 49

High photosynthetic rate

Question 50

Which have higher transpiration rates, gymnosperms or angiosperms?

Answer 50

Angiosperms

Question 51

When did the grasses spread and diversify ?

Answer 51

During global aridification

Question 52

Why was the innovation of a dumb-bell shaped stomata beneficial for grasses ?

Answer 52

Led to quicker opening/closing in the more open habitat light + water-limited conditions

Question 53

What is photorespiration?

Answer 53

When rubisco catalyses the reaction between Ribulose 1,5-bisphosphate (RuBP) and O2, instead of CO2

Question 54

Why is photorespiration bad ?

Answer 54

It wastes energy and reduces sugar production.

Question 55

What factor increases photorespiration?

Answer 55

High temperatures

Question 56

What evolved to reduce photorespiration, by making rubisco more efficient?

Answer 56

C4 photosynthesis - they separate CO₂ capture and sugar production into different cells. They use an enzyme called PEP carboxylase which only binds to CO2 and delivers it to rubisco

Question 57

What is the spread of grasses linked to?

Answer 57

Aridity, falling CO2 and fire

Question 58

Which plant accounts for 80% of the ~11,000 non-flowering vascular plant species?

Answer 58

Ferns

Question 59

Which functions must the xylem perform?

Answer 59

- water transport (mineral & carbohydrates), - mechanical support - resistance to drought

Question 60

What 3 factors are in the xylem trade off triangle ?

Answer 60

- Resistance to embolism - Conductive efficiency - Mechanical strength

Question 61

Why does fern's not having secondary growth benefit their adaptability?

Answer 61

Means they only need to adapt in 2 ways not 3 : - water transport - cavitation resistance

Question 62

Why is the fern xylem more efficient at moving water than confier xylems ?

Answer 62

Because its tracheids are longer and wider

Question 63

What affects the spread of an embolism ?

Answer 63

The vascular arrangement - more closely packed (air spreads faster)

Question 64

Why do seeds out compete ferns in dry environments?

Answer 64

- Ferns have weaker stomatal control than seeded plants (more conservative) - Ferns also lack capacitance (storage of water in stems) of seed plants that would buffer against fluctuations in water availability, leading to more rapid stomatal closure

Question 65

What is the main ignition source of natural fires ?

Answer 65

Lightning

Question 66

How can fire benefit some seeds?

Answer 66

Some cones depend on the heat of fire to open

Question 67

How did fire benefit Anigosperms over gymnosperms ?

Answer 67

Angiosperms grew faster and reproduced more quickly than gymnosperms (like pines and conifers). After a fire, angiosperms could bounce back (regrow and reseed) faster than the slower-growing gymnosperms

Question 68

Are c4 or c3 plants better adapted to fire?

Answer 68

C4