CHURCH TEACHERS’ COLLEGE

Name: Chevance Henry

I.D. #: CH20149495

Date: September 3, 2014.

Lecturer: Mr. Gad Onywere

Course Name: Plant Diversity

Course Code: SC202SEB

In partial fulfillment of the Bachelor of Science in Biology Education

Assignment #1

Question 1:

Describe the morphology and anatomy of different types of algae life forms.

(20 marks)

Question 2:

Explain how the morphology and anatomy of algae are related to their size and

habitats. (20 marks)

Question 3:

Describe the life cycle of algae (with the aid of diagrams). (30 marks)

QUESTION 1

Describe the morphology and anatomy of different algae life forms. (20 marks)

Algae survie in an aquatic marine or fresh water environment which is only restricted by the

amount of light. Mostly in its reproductive cells, it has little or no tissue differentiation. Algae

exists in four major morphological forms: unicellular, filamentous, colonial or thallose. In its

diversity. In its diversity of photosynthetic pigments all have chlorophyll; other pigments include

chlorophylls b, c, d; carotenoids (carotene, fucoxanthin, xanthophyll); biliproteins

(phycoerythrin, phycocyanin). Carotinoids and biliproteins however are restricted to algae at

greater depths where mostly blue-green wavelength light penetrates chloroplasts. Many algae

have associated pyrenoids for carbon-fixation and starch storage. Some have means of detecting

light.

Many of the unicellular species of algae have flagella with the exception of the red algae. In the

diveristy of cell wall structures most have cellulose and many secrete mulcilage. Some species

however do lack cell wall. Reproductive methods in algae have asexual of two forms (cell

division and fragmentation) and also sexual with variation in gametes types (isogamous,

anisogamous, oogamous). Variation also occurs in the life cycle patterns which include:

diplontic, haplontic and alternation of generations.

Algae is split into at least five distinct groups by several characteristics: pigments present, cell

wall structure and carbohydrate storage molecule. The first division Chlorophyta which contains

Green Algae has chlorophylls a and b, and carotenoids as apart of its photosynthetic pigments.

Its cell wall is made of cellulose and its carbohydrate storage molecule contains starch. Their

flagella vary in number. In Green Algae both fresh water and marine species have a wide

variation in size which include unicellular, filamentous, colonial and thallose. The various

species can be unicellular, multicellular, coenocytic (having more than one nucleus in a cell), or

colonial. Chlorophyta are largely aquatic or marine, a few types are terestrial, occuring on moist

soil, on trunks of trees, on moist rocks and in snow banks. Green algae are an extremely varied

group of more than 7, 000 species, mostly mobile and aquatic like Chlamydomonas, but a few

like Chlorella are immobile in moist soil or on tree trunks. Most green algae are microscopic and

unicellular, but some like Ulva (sea lettuce), are large and multi-cellular. Among the most

elaborate is Volvox, a hollow sphere made of tens and thousands of cells. The two flagella of

each cell beat in time with all the others to rotate the colony which has reproductive at one end.

Volvox borders on true multicellularity.

The second division Rhodophyta (Red Algae) have photosynthetic pigments such as chlorophylls

a and d, phycoerythrin and phycocyanin. In its cell wall cellulose secrete massive amounts of

polysaccharides, agar (microbial culture medium) and carrageenan which can be used as a

thickener in dairy products and salad dressings. Floridean starch can be found in its carbohydrate

storage molecule. No flagella are produced by any cells. Almost all of the 4, 000 species of red

algae are multi-cellular and live in the sea where they grow more deeply than other

photosynthetic organism. Red algae have complex bodies made of interwoven filaments of cells.

Members of the division of Rhodophyta have a purplish color imparted by accessory pigments

called phycobilins. Red algae are characterized by a great deal of branching but without

differentiation into complex tissues. Most of the worlds seaweeds belong to this group and they

are most common in warm-temperate and tropical climate where they may occur at great depths.

The life cycle of the algae in the division of Rhodophyta is very complex with three different

forms. The Gametophyta form where the haploid cell (1n) grows and can become quite large are

commonly separate male and female plants. The male plants produce spermatangia in which

cells divide by mitosis to produce spermatia which does not have a flagella. The female plants

produce archegonia in which eggs are produced by mitosis; after fertilization the zygotes develop

on the Gametophyte. The Carposporophyte form where the diploid cell grows and eventually

produce Carposporangia, as a result of mitosis Carpospores are produced and released. The

Tetrasporophyte form where the diploid cell develop as separate thalli which produce

tetrasporangia in which meiosis occurs to produce tetraspores of a haploid nature.

The third dvision Phaeophyta (Brown Algae) produce the largest of the algae- Kelp a type of

brown algae, can be over 100 meters long. Most brown algae are marine in cooler climates,

typically shallow waters where there is high energy for example high or low tide zones. Their

photosynthetic pigments contain chlorophylls a and c, and fucoxanthin which give them a

yellowish to brown color. They are thallose with holdfasts but a variation produce a flattened

portion (blade) and gas-filled chambers called floats. The cell wall is composed of cellulose and

alginic acid which usually extracted for food products such as food thickeners and stabilizers, ice

cream and chocolate milk. Most are isogamous with alternation of generations anywhere from

isomorphic to heteromorphic.

The fourth division Euglinophyta (Euglinoids) contain photosynthetic pigments with chlorophyll

a and b, carotenoids and some forms without chloroplasts. They do not have a cell wall but a

flexible structure of a protein called Pellicle. In its carbohydrate storage molecule it contains

paramylon and the structure contain two flagella. This common fresh water algae can produce

dense colonies or blooms in high nutrient areas such as barnyard ponds and sewage treatment

lagoons. Numerous of these specieshave a gullet which alllows for ingestion of food hence they

are heterotrophic and only about a third have the ability for photosynthesis. Contractile vacuoles

collect excess water from all parts of the organism and empty it into the reservior which

apparently helps to regulate the osmotic pressure within the organism.

The fifth division Dinophyta (dinoflagellates) contains algae with chlorophylls a and c,

peridinum which is a carotinoid that gives them a brownish color. Its cell wall contains two

grooves or furrows that are transverse and longitudinal while some cell wall contain spines and

cellulose plates. There are about 1,000 species, some occur in freshwater but most are marine.

Luminous dinoflagellates produce the twinkling light sometimes seen in tropical seas at night.

Most dinoflagellates have a stiff coat of cellulose often encrusted with silica, giving them

unusual shapes. Their flagella are unique, unlike those of any other phylum. One of the flagella

beats in a groove circling the body like a belt, the other is in a groove perpendicular to it. Their

beating flagella rotates like a top. A few dinoflagellates produce powerful toxins such as the

poisonous ‘red tides’, which are population explosions of such dinoflagellates. Dinoflagellates

reproduce by spliting in half. Their form of mitosis is unique due to the fact their chromosomes

remain condensed and distributed along the side channels containing bundles of microtubles that

run through the nucleus.

QUESTION 2

Explain how the morphology and anatomy of algae are related to their size and habitats. (20

marks)

Algae are simple structured autotrophic organisms; some are unicellular while others multi-

cellular and most photosynthesize like plants. Algae date back over billion years and some of the

first plants on earth evolved from algae. Green algae are by far the most complex group and have

led to the evolution of land plants. Their simple structure means they are lacking many

anatomical structures that true plants have, specifically organs. Algae do not have true roots but

attach to the substrate by rhizoids and rhizomes. Some species, particularly brown algae, contain

gas bladders to keep them afloat. Many types of algae are microscopic, occurring in single cells

or small colonies. The usual habitat of many of the microscopic algae is open waters, in which

case they are known as phytoplankton. Many species, however, live on the surfaces of rocks and

larger plants within shallow-water habitats, and these are known as periphyton. Other

microscopic algae live on the moist surfaces of soil and rocks in terrestrial environments.

Microscopic algae are at the base of their ecological food web; these are the photosynthetic,

primary producers that are fed upon by herbivores. In the open waters of ponds, lakes, and

especially the vast oceans, the algal phytoplankton is the only means by which diffuse solar

radiation can be fixed into biological compounds. In these open-water or pelagic zone habitats,

the phytoplankton are consumed by small, grazing animals known as zooplankton, most of

which are crustaceans. The zooplanktons are in turn fed upon by larger zooplanktons or by small

fish, these predators are known as planktivores, which may then be eaten by larger fish or

piscivores. At the top of the open-water food web may be fish-eating birds, seals, whales, very

large fish such as sharks or blue fin tuna, or humans. Therefore, the possibility of all of the

animals occurring higher in the food webs, including the largest of the top predators, are

ultimately dependent on the productivity of the microscopic phytoplankton of the pelagic marine

ecosystem.

Other algae are macroscopic, meaning they can be readily observed without the aid of

magnification. Some of these algae are enormous, with some species of kelps commonly

reaching lengths greater than tens of meters long. Because they are primary producers, these

macroscopic algae are also at the base of their ecological food webs. In most cases, however,

relatively few herbivores can directly consume the biomass of macroscopic algae, and the major

trophic interaction of these plants is through the decomposer, or detritivore part of the food web.

In addition, because of their large size, macroscopic algae are critically important components of

the physical structure of their ecosystems, providing habitat for a wide range of other organisms.

The largest kelps develop a type of ecosystem that is appropriately referred to as a marine

"forest" because of the scale and complexity of its habitat structure.

Some species of green algae occur as mutualistic symbionts with fungi, in an association of two

organisms known as lichens. Lichens are common in many types of habitats. Other green algae

occur in a mutualism with certain animals. In general, the host animal benefits from access to the

photosynthetic products of the green alga, while the alga benefits from protection and access to

inorganic nutrients. For example, species of unicellular Chlorella live inside of vacuoles within

host cells of various species of freshwater protozoan, sponges, and hydra. Another species of

green alga, Platymonas convolutae, occurs in cells of a marine flatworm, Convoluta roscoffensis.

Various other green algae occur inside of marine mollusks known as nudibranchs. Similarly,

various species of dinoflagellates occur as symbionts with marine corals.

Each species within an algal community has its particular ecological requirements and

tolerances. Consequently, algal species tend to segregate along gradients in time and space,

according to varying patterns of environmental resources, and of biological interactions, such as

competition and predation. For example, during the growing season there is a time when varying

abundances of phytoplankton species are in open-water habitat. At certain times, particular

species or closely related groups of species are abundant, but then these decline and other species

of phytoplankton become dominant; it may vary significantly from year to year. The reasons for

these patterns in the abundances and productivity of algal species are not understood, but they

are likely associated with differences in their requirements for nutrients and other environmental

factors, and perhaps with differing competitive abilities under resource-constrained conditions.

In a similar way, species of seaweeds tend to sort themselves out along stress-related

environmental gradients associated with varying distances above and below the high-tide mark

on rocky marine shores. The most important environmental stress for intertidal organisms is

desiccation (drying), caused by exposure to the atmosphere at low tide, with the intensity of

drying being related to the amount of time that is spent out of the water, and therefore to the

distance above the high-tide line. For sub-tidal seaweeds the most important stress is the physical

forces associated with waves, especially during storms. The various species of brown and red

algae are arranged in rather predictable zonations along transects perpendicular to rocky shores.

The largest kelps only occur in the sub-tidal habitats, because they are intolerant of desiccation.

Within this near-shore habitat the species of algae are arranged in zones on the basis of their

tolerance to the mechanical forces of wave action, as well as their competitive abilities in the

least stressful, deeper-water habitats somewhat farther out to sea, where the tallest species grow

and develop a kelp forest. In the intertidal, the various species of wracks and rockweeds

dominate particular zones at various distances from the low-tide mark, with the most desiccation-

tolerant species occurring closest to the high-tide mark. Competition, however, also plays an

important role in the distributions of the intertidal seaweeds.

The most abundant and commonly recognized algae on tropical reefs are the green algae. There

are many species and most are calcareous, contributing a large amount of calcium carbonate to

the reef building process. These plants form the base of the ocean food chain by carrying out

photosynthesis. Chlorophyll is the pigment that forms their various shades of green color from

bright Kelly green to yellow and brown-green to Dark green. Typically they appear as a flexible

string of flattened leaf-like structures often referred to as segments. Each segment is a deposit of

calcium carbonate covered by the algal protoplasm and connected to its neighbors by a thin

strand, giving the plant its flexibility. They are fast growing and decorative and the calcified

leaves are an integral component as the major contributor of calcium carbonate to the reef sand.

Brown algae grow into abundant coverage, often in shallow waters. They are multi-cellular

organisms and generally bushy plants formed by blunted blades, often irregularly branched.

Some kelp can grow up to 60 meters long and are the most abundant species of algae. Red algae

are often abundant but difficult to recognize due to dull coloration and their simple encrusting

growth patterns yet they are the most diversified with over 5,000 tropical species. Many are a

calcareous species and play an important role in coral reef construction. They range from dull red

to purple to dark brown-red coloration; the red pigment phycoerythrin is responsible. Most red

algae are multi-cellular and undergo sexual reproduction unlike some of the other groups.

Coralline algae prefer shade and encrust solid substrates. Colonies can be brittle and hard to

distinguish from one another.

QUESTION 3

Describe the life cycle of algae (with the aid of diagrams). (30 marks)

Reproductive methods in algae are very complex and occur asexually in two forms,

(fragmentation and cell division) and also sexually with variation in gamete types to include

isogamous (male and female sex cells are identical), anisogamous (male sex cell is smaller than

female sex cell) and oogamous (female sex cell is non-motile and male sex cell is motile).

Variation also occurs in the life cycle patterns which include diplontic, haplontic and alternation

of generations. Asexual or vegetative reproduction is common and may be more important than

sexual reproduction in most species. Sexual reproduction is least common because the

production of gametes is the prime event in sexual reproduction. Gametes from two different

individuals fuse, so that the new generation contains genetic information from both parents.

Genetic variation is thus ensured generation after generation. Cells of seaweeds and other multi-

cellular organisms divide and produce identical cells by mitosis. Seaweeds may also produce

haploid spores or gametes by meiosis.

The life cycle histories of seaweeds can be divided into four basic types. The first type (Figure 1)

is the most common among all three groups of seaweeds, and involves two types of thalli. The

first is a diploid (2n) sporophyte generation that through meiosis produces not gametes but

haploid (n) spores. Except in red algae (Figure 2), these spores are typically motile. They divide

and develop into the second kind of thallus, a haploid (n) gametophyte generation. The

gametophyte is the one that produces haploid gametes. In some species there are separate male

(sperm-producing) and female (egg-producing) thalli; in others, both types of gametes are

produced by every thallus. The gametes are released and, on fertilization, produce diploid (2n)

zygote that develops into the diploid sporophyte. This life cycle is an example of the

phenomenon of alternation of generations. In some algae, such as sea lettuce (Figure 1), the

sporophyte and gametophyte are structurally identical. On the other hand, in kelps (Laminaria,

Macrocystis and others) the large plant seen is the sporophyte, whereas the gametophyte is small

and barely visible.

The second life cycle history is unique to the red algae and is more complex because it involves

three generations (Figure 2). It is similar to the life cycle history of the seaweed in Figure 1, but a

third generation, a diploid carposporophyte, results from the fusion of gametes. Carpospores are

diploid spores produced by the carposporophyte and develop into sporophytes.

The third life cycle history (Figure 3) is similar to that of animals including humans. There is no

alternation of generations and thus, there is only one thallus, and it is diploid. The thallus

produces haploid gametes by meiosis. After fertilization the resulting zygote develops into a new

diploid thallus. This type of life cycle is most prevalent in brown algae and rockweed (Figure3)

and in some green algae.

The fourth life cycle history, which occurs in some green algae (figure 4); the dominant thallus is

haploid and produces haploid gametes. On fertilization the gametes form a diploid zygote. It is in

the zygote where meiosis takes place, resulting in haploid spores. Each of these spores develops

into a haploid individual which is the only kind of thallus in the cycle.

It is important to mention that the development of gametes or spores can be influenced by the

amounts of nutrients in the water, by temperature, or by day length. High levels of nitrogen

nutrients in the water cause the development of asexual spores in sea lettuce, but low levels

stimulate the development of gametes instead. The release of gametes and spores can be

triggered by the splashing of water in an incoming tide or by chemical messengers received from

cells of the opposite sex. In some seaweed the release of the male and female gametes is timed to

take place at about the same time.

References

Toole, G. & Toole, S. (1995). Understanding Biology for Advanced Level (Third Edition).

Stanley Thornes Publishers Ltd.

Johnson, George B. (2003). The Living World (Third Edition). McGraw-Hill Higher Education

Castro, Peter & Huber, Michael E. (2007). Marine Biology (Seventh Edition).McGraw-Hill

Higher Education

Lenntech, B.V (2014). Algae description and types. Retrieved

from:http://www.lenntech.com/eutrophication-water-bodies/algae.htm#ixzz3BeAkdNWq

Taylor, Jason deCaires. Underwater sculpture. Retrieved from: http://www.underwatersculpture.com/environment/algae/

Net Industries (2014). Factors Limiting the Productivity of Algae. Retrieved from: http://science.jrank.org/pages/202/Algae-Factors-limiting-productivity-algae.html