Practical 29 Marine Biology CAPS block 25 · Term 3 · 4 hours

Porifera — the Sponges

Find sponges where they hide, and watch them pump. Work out what a sponge skeleton is made of without touching a drop of acid. Put numbers on how much water one small sponge can filter. Then do the booklet's own labelling and adaptations tasks.

What CAPS asks for

Investigations column, block 25: "Photographs, slide show or videos · Study live examples (aquarium or rock-pool study) · Observation of as many live species as possible · Use one specific locally available example · Incorporate into ecosystem field trips · Isolate spicules for study under microscope, by dissolving sponge fragments in nitric or sulphuric acid."

The rock-pool study is Investigation 1. The spicule method is Investigation 2 — with supplied results, because nitric and sulphuric acid are school-laboratory chemicals that must never be used at home. Investigation 3 puts numbers on CAPS key concept 8 ("sponges are very effective ecological filters"), and Investigation 4 is the booklet's labelling and adaptations questions.

What you need

🌊 shore A rock pool with loose boulders at spring low tide — Cape Recife, Sardinia Bay or any rocky shore
🟢 kitchen A notebook, a ruler, your phone camera, a plastic dropper or straw, and food colouring (or a little milk)
🟢 kitchen A calculator, graph paper, a sharp pencil and coloured pencils
🟡 optional A hand lens, to see a sponge's pores and oscula
🔴 lab only Nitric or sulphuric acid and a microscope, for isolating spicules — supplied as results; do not attempt

You will not have the acid — and you must not try to get it. That's fine.

Investigation 2 gives you a laboratory's results to analyse instead. Investigation 1 has described sponges and a described flow test if you cannot get to the shore. Investigations 3 and 4 are desk tasks with everything supplied.

Safety — the shore, and the chemicals you are not using On the shore: work only on a falling tide, never alone, and never turn your back on the sea. Some sponges irritate the skin — touch them with a stick, not your fingers, and do not rub your eyes. Turn every boulder back exactly as you found it. Strong acids burn skin and eyes and give off dangerous fumes; they belong in a school laboratory with a fume cupboard and a teacher. And never mix bleach with any acid, including vinegar — together they release poisonous chlorine gas.

1 The Rock-Pool Sponge Study CAPS Investigation: "study live examples (aquarium or rock-pool study)"

Aim

To find and describe live sponges in their habitat, and to observe the direction of water flow through a sponge.

Method

At spring low tide, search rock-pool walls, crevices and overhangs. Gently roll a few loose boulders over and look at their shaded undersides.
For each sponge you find, record its colour, growth form (crust, cushion, lobes, fingers, vase), approximate size, texture (test with a stick), whether you can see oscula, and where it is growing. Photograph it beside a ruler.
The flow test. Choose an underwater sponge in calm water. With a dropper, release one drop of food colouring (or milk) in the water right beside its surface. Watch closely for a minute: where does the colour go?
Turn every boulder back exactly as it was.

Supplied data — four sponges and a flow test from a south-coast rock pool

Sponge 1 An orange crust about 8 cm × 5 cm and 2 mm thick on the underside of a boulder. Covered in tiny pores, with six small raised oscula 1–2 mm across. Rough and gritty to the stick.

Sponge 2 A grey-green lobed sponge 6 cm tall, wedged in a crevice. A large osculum, 3–4 mm across, on the top of each lobe. Firm, with a strong smell.

Sponge 3 A small white vase 2 cm tall under an overhang, with one osculum at the top fringed by tiny bristles (spicules). Very fragile.

Sponge 4 A yellow cushion 4 cm across on the pool floor. Its surface is dusted with silt everywhere except in clean patches around each osculum.

Flow test on Sponge 2. The drop of colouring placed beside the sponge's side was drawn towards and into its surface within about two seconds, and no colour came back out through the side. About 20 seconds later, faint coloured water rose in a gentle jet from the oscula on top of the lobes, and the cloud above them was pushed upwards and away. A drop of milk behaved the same way; the water rising from the oscula looked clearer than the milky water around the sides.

Results

Table 1.1 — sponges observed
Sponge	Colour	Growth form	Symmetry	Oscula?	Where growing
1
2
3
4

Analysis

Complete Table 1.1 for four sponges — your own, or the supplied ones. 8
The four sponges have very different shapes, yet all are described as having the same symmetry. Name it, and explain why the different shapes do not change the answer. 2
Most of the sponges were on the undersides of boulders, in crevices or under overhangs. Suggest three reasons. 3
Sponge 4 was dusted with silt everywhere except around its oscula. Explain why. 2
Describe the evidence from the flow test that water moves one way through a sponge. Explain what drives the flow. 4
Why did the water rising from the oscula look clearer than the milky water around the sides? 2
Why can't you name these sponges to species from these observations? What would a specialist examine? 2
Why must each boulder be turned back exactly as it was? 2

2 Spicules — the CAPS Method, Made Safe CAPS Investigation: "isolate spicules … by dissolving sponge fragments in nitric or sulphuric acid"

Aim

To identify what three sponges' skeletons are made of from laboratory results, to measure their spicules, and to judge the CAPS method.

What the laboratory did

A school laboratory took small fragments of three sponges, X, Y and Z, and did two tests on each. ① The fragment was soaked in household bleach overnight, which dissolves the soft cells, and the residue was examined under a microscope. ② A drop of dilute acid was added to the residue under the microscope. Spicules were measured with a scale in the eyepiece.

Supplied results — sponges X, Y and Z

Data set 2.1 — observations
Sponge	After bleach	When acid was added
X	a white sediment of three-rayed spicules and a few straight needles	tiny bubbles formed at once; within a minute every spicule had disappeared
Y	a sediment of clear, glassy needles pointed at both ends, and a few small star shapes	no bubbles; the spicules were unchanged after ten minutes
Z	(before bleach, under the microscope: a tangled mesh of flexible, yellowish fibres, no hard spicules) — after a day in bleach the fibres had slowly broken down	no bubbles; the fibres were unchanged

Data set 2.2 — lengths of fifteen needles from sponge Y (micrometres, µm)
212	198	225	240	205	218	231	190	222	209	236	214	201	228	216

Data set 2.3 — lengths of one ray on ten three-rayed spicules from sponge X (µm)
95	110	102	88	120	105	98	112	91	108

1 000 micrometres (µm) = 1 millimetre (mm).

Analysis

Identify what the skeleton of each sponge — X, Y and Z — is made of. Give the evidence for each. 6
Calculate the mean and the range of the needle lengths for sponge Y and of the ray lengths for sponge X. Give Y's mean in millimetres too. 5
CAPS suggests isolating spicules by dissolving sponge fragments in nitric or sulphuric acid. Which of these sponges' skeletons would survive that treatment, and which would be destroyed? Explain. 4
Why did the laboratory use bleach, rather than acid, to free the spicules of sponge X? 2
Give two reasons why strong acids belong only in a school laboratory, and explain why bleach and acid must never be mixed. 3
Draw one needle from sponge Y and one three-rayed spicule from sponge X, and label each with its material. 4
Why do specialists measure many spicules from a sponge, rather than one, when identifying it? 2

3 How Much Can a Sponge Filter? CAPS key concept 8: "sponges are very effective ecological filters"

Aim

To calculate how much water a sponge pumps, from the size of its osculum and the speed of the water leaving it.

The data

Scientists measure a sponge's pumping by releasing dye just below the osculum and timing how fast it is carried upwards. The flow rate is then the area of the osculum × the speed of the jet.

Data set 3.1 — two sponges
Sponge	Description	Osculum diameter	Jet speed
A	a small tube sponge, 10 cm tall and 1 cm across	4 mm	2.0 cm/s
B	a giant barrel sponge on a tropical reef	10 cm	5.0 cm/s

Useful formulas. Area of a circle = π r², with π = 3.14. Volume of a cylinder = π r² h. 1 cm³ = 1 mL, and 1 000 cm³ = 1 litre. There are 86 400 seconds in a day.

Analysis

Calculate the area of sponge A's osculum in cm². 2
Calculate sponge A's flow rate in cm³ per second, and then in litres per day. 4
Treat sponge A as a cylinder. Calculate its volume, and how many seconds it takes to pump a volume of water equal to its own body. 3
A rock pool holds 500 litres and contains twenty sponges like sponge A. How long would they take to filter a volume of water equal to the whole pool? 3
Calculate sponge B's flow rate in litres per day. 3
Explain why sponges matter to the clarity of reef water and to the other animals living there — and predict what happens to a reef if trawling destroys its sponges. 3
Suggest one source of error in measuring the jet speed with dye, and how to reduce it. 2

4 Label It and Tabulate It the booklet's "Test your knowledge" questions 1–3 · CAPS: "use labelled diagrams"

Aim

To draw and label the sponge's body wall and a collar cell, and to summarise the sponge's adaptations.

Your diagrams

Analysis

Draw a cross-section of a sponge's body wall, with the outside on the left and the central cavity on the right, and label: outer dermal layer, mesenchyme, inner layer of collar cells, spicule, amoeboid cell, pore cell, spicule-producing cell. (7 labels, plus 3 for an accurate, neat drawing.) 10
Draw a single collar cell and label the body of the cell, collar, flagellum, trapped food particles and food vacuole. Add arrows showing the direction of water flow. 6
Tabulate the specific adaptations of sponges under the headings body symmetry, protection, support, nutrition, nervous coordination and internal transport. For each, give one adaptation and explain how it helps. 12
Give the scientific term for: (a) sex cells that fuse to form a zygote; (b) able to produce both male and female gametes; (c) a jelly-like layer between the outer dermal and inner collar-cell layers of a sponge, containing scattered cells and spicules. 3

Memo — worked answers and mark allocation (does not print)

Total: 102 marks — Investigation 1: 25 · Investigation 2: 26 · Investigation 3: 20 · Investigation 4: 31.

Investigation 1 — rock-pool study

Q1 (8): Two marks per sponge for an accurate row. Supplied: 1 orange · crust · asymmetrical · yes, six small · underside of a boulder. 2 grey-green · lobed · asymmetrical · yes, large, on lobe tops · crevice. 3 white · vase · asymmetrical (accept "roughly radial vase, but still classed asymmetrical") · one, at the top · under an overhang. 4 yellow · cushion · asymmetrical · yes · pool floor.
Q2 (2): Asymmetrical (1). A sponge grows continuously to fit the space and water flow where it lives, so its shape varies, but no plane divides any of them into mirror halves (1).
Q3 (3): Any three: protection from drying out and sun at low tide; protection from waves; less competition from seaweeds, which need light and take the open rock; shelter from grazers and predators; silt settles less on downward-facing surfaces.
Q4 (2): Water leaving the oscula flows outward and upward (1), so silt cannot settle there — and particles near the inlet pores are drawn in and filtered (1).
Q5 (4): The dye was drawn into the sides and came out only from the oscula, never back out of the sides (2). The beating flagella of the collar cells drive water in through the pores and out of the oscula (2).
Q6 (2): The collar cells trapped the milk particles as the water passed through (1) — the sponge filtered them out, so the outgoing water was cleaner (1).
Q7 (2): Shape and colour vary with where a sponge grows, so they are unreliable (1); a specialist examines the cells and especially the spicules, whose shapes are often species-specific (1).
Q8 (2): The sponges and other animals under it need the shade, moisture and shelter of that surface (1); left upside down they would dry, overheat or be eaten, and the upper surface's seaweeds would be smothered (1).

Investigation 2 — spicules

Q9 (6): X — calcium carbonate (1): it fizzed and dissolved in acid, as carbonates do (1). Y — silica (1): glassy, and unchanged by acid (1). Z — spongin (1): flexible protein fibres with no hard spicules, unaffected by acid but broken down by bleach (1).
Q10 (5): Y: sum 3 245 ÷ 15 = 216.3 µm (1); range 190–240 µm (50 µm) (1); 216.3 µm = 0.216 mm (1). X: sum 1 029 ÷ 10 = 102.9 µm (1); range 88–120 µm (32 µm) (1).
Q11 (4): Y's silica spicules would survive (1), because silica does not react with these acids (1). X's calcium carbonate spicules would be destroyed — the acid dissolves them along with the tissue (1). Z's spongin would survive the acid briefly but is not a spicule skeleton (1). So the CAPS method isolates only silica spicules.
Q12 (2): Bleach dissolves the soft tissue (1) but does not attack calcium carbonate, so the chalky spicules are left behind (1).
Q13 (3): Strong acids burn skin and eyes; their fumes are dangerous to breathe; they need a fume cupboard and trained supervision (any two, 2). Bleach and acid together release poisonous chlorine gas (1).
Q14 (4): A straight needle pointed at both ends, labelled "silica" (2); a spicule with three equal rays at about 120°, labelled "calcium carbonate" (2).
Q15 (2): Spicules vary in size and shape even within one sponge (1), so a mean and range from many give a reliable description to compare with known species (1).

Investigation 3 — filtering

Q16 (2): r = 0.2 cm (1); area = 3.14 × 0.2² = 0.126 cm² (1).
Q17 (4): Flow = 0.126 × 2.0 = 0.251 cm³/s (2). Per day: 0.251 × 86 400 = 21 700 cm³ (1) = about 21.7 litres/day (1). Matches the classic textbook figure of about 22 L for a sponge this size.
Q18 (3): Volume = 3.14 × 0.5² × 10 = 7.85 cm³ (1). Time = 7.85 ÷ 0.251 = about 31 seconds (2).
Q19 (3): 20 × 21.7 = 434 L/day (1). 500 ÷ 434 = about 1.15 days (1) — roughly 28 hours (1).
Q20 (3): Area = 3.14 × 5² = 78.5 cm² (1). Flow = 78.5 × 5.0 = 392.5 cm³/s (1). Per day: 392.5 × 86 400 ≈ 33 900 000 cm³ = about 33 900 litres (1).
Q21 (3): Sponges remove almost all suspended particles, keeping the water clear so light reaches seaweeds and corals (1); they recycle nutrients and their bodies shelter other animals (1). Destroying them leaves murkier water, fewer shelters and less recycling, harming the whole reef (1).
Q22 (2): E.g. the dye spreads as it rises, so its front is hard to time; the observer's reaction time; currents add to or slow the jet (1). Improvement: film it beside a scale and measure frame by frame, repeat and average, work in still water (1).

Investigation 4 — label and tabulate

Q23 (10): One mark per correctly placed label (7): dermal layer on the outside; mesenchyme in the middle; collar cells lining the inside with flagella pointing into the cavity; spicule in the mesenchyme; amoeboid cell in the mesenchyme; pore cell forming a tube right through the wall; spicule-producing cell with a spicule forming inside it. Drawing quality (3): clear lines, correct order of layers, label lines ruled.
Q24 (6): Five labels (5) and arrows showing water drawn in through the collar and pushed out along the flagellum, away from the cell (1).
Q25 (12): Two marks per heading — the adaptation (1) and how it helps (1). Symmetry: asymmetrical — grows to fit its space, filters from all around. Protection: dermal layer and sharp spicules, often with warning colours — deters grazers. Support: mesenchyme with a spicule lattice — a framework the layers hang on. Nutrition: filter feeding by collar cells — they drive the current and trap food. Nervous coordination: none — it does not move, so it needs none. Internal transport: diffusion between cells, helped by amoeboid cells — no cell is far from the water flow.
Q26 (3): (a) gametes · (b) hermaphroditic · (c) mesenchyme.

Marking note. Q11 is the question this sheet exists for: the CAPS method dissolves calcium carbonate, so it can only ever isolate silica spicules. A learner who spots that has understood both the chemistry and the limits of a method — reward it fully however it is worded.