LEC 1: ENDOSYMBIOSIS, CHLOROPLASTS, LAND

Question 1

What is an advantage of having a nucleus in plants (or any Eukaryotes)

Answer 1

Being able to distinguish between sites for transcription and translation ensures controlled protein expression and coordination with the cell cycle.

Question 2

Briefly explain what occurs when plants photosynthesize

Answer 2

Plants take water, air and light and convert it to organic molecules (in the form of carbon/hydrogen) or sugars

Question 3

Why would plants store the energy they harvest in the form of organic molecules/sugars?

Answer 3

When carbon bonds in sugar are broken there is a large energy release. (The energy is used to power other processes)

Question 4

What is the greatest advantage of being a multicellular organism?

Answer 4

There is a division of labor which allows groups of cells to focus on a single, designated function

Question 5

Describe what alternating generations are in plants

Answer 5

• Refers to the different stages a plant is in during its life cycle.
• Can be either gametophyte or sporophyte/ haploid or diploid.

Question 6

How many sets of chromosomes do gametophytes and sporophytes have respectively?

Answer 6

• Gametophytes are haploid and contain a single set of chromosomes
• Sporophytes are diploid and contain two sets of chromosomes

Question 7

What is a key difference in the animal and plant reproductive cycle?

Answer 7

• In animals, a haploid cell will only remain haploid for a short period of time – it will get fertilized and turn into a diploid zygote quickly.
• Plants can remain the haploid stage for much longer, the length being dependent on the evolutionary progression of the species (some plants can stay longer as haploid than others)

Question 8

What are the 4 main photosynthesizing plant types and what differentiates them

Answer 8

1. green algae: photosynthesize but are aquatic
2. non vascular seedless bryophytes: land plants, but lack any vascular mechanisms (xylem/phloem) so often grow low to the ground.
3. vascular seedless plants: have vascular systems but do not have seeds.
4. vascular seed plants: have vascular systems and seeds.

Question 9

What was the progenitor of chloroplasts?

Answer 9

Cyanobacteria

Question 10

Was the progenitor of chloroplasts prokaryote or eukaryote?

Answer 10

It was Cyanobacteria, so prokaryote

Question 11

What process allowed for chloroplasts to become a part of plant cells?

Answer 11

Endosymbiosis, or the engulfment of bacteria without destruction. The process that allows a living thing to be inside a dissimilar organism.

Question 12

What two organelles are descendants of endosymbiosis?

Answer 12

Mitochondria and chloroplasts.

Question 13

Do cyanobacteria have nuclei?

Answer 13

No, they are prokaryotic

Question 14

What features of cyanobacteria were so important for land plants to have?

Answer 14

Cyanobacteria could photosynthesize using thylakoids and chlorophyll.

Question 15

What are thylakoids and what purpose do they serve in plant photosynthesis?

Answer 15

Thylakoids are repeated folds of membrane, and are the site of protein complexes/reactions required for light energy production.

Question 16

What is chlorophyll and what purpose does it serve in plant photosynthesis?

Answer 16

Chlorophyll is a pigment that absorbs light energy used for photosynthesis.

Question 17

Where in the plant cell/cyanobacteria is chlorophyll found?

Answer 17

Thylakoids

Question 18

Do prokaryotes have cyanobacteria or mitochondria?

Answer 18

No, because both are already prokaryotic. Eukaryotes may have either through endosymbiosis.

Question 19

What is an endosymbiont, provide an example of one

Answer 19

An endosymbiont is a captured prokaryotic cell that was engulfed by a eukaryotic cell.

Cyanobacteria is an endosymbiont and became the chloroplast in plants.

Question 20

Why would organelles like the chloroplast and mitochondria have their own genome/DNA?

Answer 20

Because both were once their own prokaryotic cells containing DNA.

Ex. Chloroplasts were once cyanobacteria which has its own free floating DNA.

Question 21

What does obligate endosymbiosis mean?

Answer 21

The host cell requires/depends on the endosymbiont/organelle.

Question 22

What 2 solutions did plants adapt to combat desiccation/drying out?

Answer 22

1. Plants reduced their surface area to volume ratio to keep their large internal space without losing its content to the environment.
2. Plants also developed multicellularity, where cells had defined functions to combat secondary issues involved with moving on land (Ex. stomata cells for gas exchange, cuticle cells for protection etc).

Question 23

What solution did plants develop to combat the issue of differing gas absorption on land vs in water.

Answer 23

Plants developed a new system of gas exchange - the stomata - which can open and close when necessary.

Question 24

What solution did plants develop to replace zoospores, or swimming/motile sex cells for reproduction on land?

Answer 24

Plants developed spores and seeds for reproduction on land, which can be dispersed without having to be motile.

Question 25

What solution did plants develop to replace buoyancy on land?

Answer 25

Plants developed strong fibers made of lignin and cellulose that acted like a skeleton/supported the plant.

Question 26

What solution did plants develop to combat the absorption of light wavelengths and harmful UV rays.

Answer 26

Pigments that absorb UV rays (separate to chloroplasts) removed the harmful rays and left only wavelengths that could be absorbed by the chloroplast.

Question 27

What solution did plants develop to combat mineral absorption on land?

Answer 27

Plants developed roots which could absorb dissolved minerals from the soil.

Question 28

What are the 2 species that evolved from green algae?

Answer 28

Liverworts and Mosses