What is Reproduction & development on the Living Environment Regents?

Reproduction & development is a Human Systems topic on the Living Environment Regents. RegentsLab has 20 practice questions on it, each with a full worked solution.

Reproduction & development: Living Environment Regents Practice

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Work a range of Reproduction & development question types and read the worked solution every time you miss one — the exam reuses the same ideas year after year. Start with the questions on this page.

Practice Reproduction & development for the Living Environment Regents with real-style questions and full worked solutions. Miss one? Read the solution — the exam reuses the same ideas every year.

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Question 81 · 2 pts

In humans, a normal body cell contains $46$ chromosomes. As a direct result of meiosis, a normal human egg cell or sperm cell contains how many chromosomes?

(A) $46$
(B) $92$
(C) $0$
(D) $23$ ✓

Worked solution

$\text{body cell (diploid)} = 46$ Starting chromosome number.

$46 \div 2 = 23$ Meiosis halves the chromosome number to make gametes.

Answer: $23$

Meiosis reduces the chromosome number by half, producing gametes with a single set so that fertilization can restore the species chromosome number.

Question 83 · 2 pts

A hydra reproduces by forming a bud that grows and then detaches as a new individual. The offspring produced in this way are

(A) genetically identical to the parent ✓
(B) formed by the fusion of two gametes
(C) genetically identical to one another but different from the parent
(D) more genetically varied than the parent

Worked solution

$\text{budding} \Rightarrow \text{mitosis}$ One parent, division by mitosis.

$\text{mitosis} \Rightarrow \text{identical DNA}$ Mitosis copies the full genome exactly.

Answer: genetically identical to the parent

Budding is asexual reproduction based on mitosis, so the offspring are clones carrying the same genetic information as the single parent.

Question 94 · 2 pts

Many fish reproduce by external fertilization, releasing thousands of eggs and sperm into the water at the same time. Producing such large numbers of gametes most directly increases the chance that

(A) each unfertilized egg will divide by meiosis to form a new fish.
(B) the adult fish will grow much larger after spawning.
(C) the offspring will be genetically identical to one parent.
(D) sperm and eggs will meet in the water so that fertilization can occur. ✓

Worked solution

$\text{many gametes in water} \Rightarrow \uparrow\ P(\text{sperm meets egg})$ External fertilization happens in open water, where many gametes are lost.

$\text{more contacts} \Rightarrow \text{more fertilizations}$ Large gamete numbers raise the chance that fertilization occurs.

Answer: sperm and eggs will meet in the water so that fertilization can occur.

In external fertilization gametes are released into water, where many are lost, so producing large numbers raises the probability that sperm and eggs meet and fertilization occurs.

Question 96 · 2 pts

A fertilized human egg (zygote) divides again and again to form the many cells of an embryo. Which statement correctly describes these divisions?

(A) Each division fuses two cells together, so the chromosome number doubles every time.
(B) Each new cell is produced by mitosis and has the same chromosome number as the zygote. ✓
(C) The cells lose chromosomes with each division, so later cells have fewer genes.
(D) Each new cell is produced by meiosis and has half the chromosome number of the zygote.

Worked solution

$\text{zygote} \xrightarrow{\text{mitosis}} 2 \rightarrow 4 \rightarrow 8 \rightarrow \dots \text{cells}$ Embryonic growth and development occur by repeated mitosis.

$\text{chromosome number per cell} = \text{constant (diploid)}$ Mitosis keeps the full chromosome number in every new cell.

Answer: Each new cell is produced by mitosis and has the same chromosome number as the zygote.

Growth and development of an embryo occur by mitotic cell division, which produces genetically identical cells, each carrying the same full chromosome number as the original zygote.

Question 20 · 2 pts

In humans, body cells contain 46 chromosomes. During the formation of sperm and egg cells, the chromosome number is reduced by half so that each gamete contains 23 chromosomes. This reduction occurs during

(A) fertilization
(B) cloning
(C) mitosis
(D) meiosis ✓

Worked solution

$Body (somatic) cells are diploid, containing two sets of chromosomes (46 total in humans).$ Diploid number

$Gametes must be haploid so that when two gametes join, the normal diploid number is restored.$ Purpose of reduction

$Meiosis is the type of cell division that reduces the chromosome number by half, producing haploid gametes.$ Definition of meiosis

$Mitosis keeps the chromosome number the same and is used for growth and repair, not gamete formation.$ Distinguish from mitosis

Answer: meiosis

Meiosis is the specialized cell division process that reduces the chromosome number by half, producing haploid gametes (sperm and egg) so that fertilization restores the normal diploid chromosome number in offspring.

Question 57 · 4 pts · constructed response

Describe the function of the placenta during human pregnancy, and explain why this structure is important for the survival and development of the fetus.

Model answer: The placenta allows the exchange of materials between the mother's blood and the developing fetus's blood, providing the fetus with oxygen and nutrients and removing carbon dioxide and other wastes. This exchange is important because the fetus cannot obtain nutrients or eliminate wastes on its own, so without the placenta the fetus could not grow and develop properly.

Worked solution

$\text{Placenta connects mother's blood supply and fetal blood supply}$ Structure/location

$\text{Nutrients and oxygen diffuse from mother to fetus}$ Function 1

$\text{Wastes (CO2, urea) diffuse from fetus to mother for removal}$ Function 2

$\text{Fetus depends on this exchange for growth and development}$ Importance

Answer: The placenta allows the exchange of materials between the mother's blood and the developing fetus's blood, providing the fetus with oxygen and nutrients and removing carbon dioxide and other wastes. This exchange is important because the fetus cannot obtain nutrients or eliminate wastes on its own, so without the placenta the fetus could not grow and develop properly.

The placenta is the organ of exchange between mother and fetus, supplying nutrients and oxygen while removing wastes, functions the fetus cannot yet perform for itself.

Question 18 · 1 pt

Compared with asexual reproduction, sexual reproduction usually results in offspring that

(A) have half the chromosomes of normal body cells
(B) are genetically identical to one parent
(C) show greater genetic variation ✓
(D) cannot adapt to the environment

Worked solution

$\text{two parents} \Rightarrow \text{new combinations}$ Meiosis + fertilization mix genes.

Answer: \text{greater variation}

Sexual reproduction combines genes from two parents, producing varied offspring, raw material for adaptation and evolution.

Question 82 · 2 pts

The joining of a sperm and an egg during fertilization produces a zygote that

(A) has half the chromosome number found in a body cell
(B) contains genetic information from the mother only
(C) contains genetic information from two parents and the full species chromosome number ✓
(D) is genetically identical to each of its parents

Worked solution

$\text{egg } (n=23) + \text{sperm } (n=23)$ Two haploid gametes unite.

$\Rightarrow \text{zygote } (2n=46)$ Fertilization restores the diploid number and merges both parents' genes.

Answer: genetic information from two parents and the full chromosome number

Fertilization fuses two haploid gametes, restoring the diploid chromosome number and combining genes from both parents, which is a source of variation.

Question 84 · 2 pts

All of the body cells in a multicellular organism contain the same genetic information, yet a muscle cell differs in structure and function from a nerve cell. This specialization (differentiation) occurs because

(A) gametes supply each cell type with its own unique genes
(B) each cell type receives a different set of genes during mitosis
(C) specialized cells lose the genes they do not use
(D) different genes are expressed, or turned on, in different types of cells ✓

Worked solution

$\text{all cells: same DNA}$ Mitosis gives every cell the full genome.

$\text{selective gene expression} \Rightarrow \text{different proteins}$ Different active genes build different cell types.

Answer: different genes are expressed in different cells

Differentiation results from different portions of the identical genetic code being activated in different cells, leading to different proteins and specialized structures.

Question 85 · 2 pts

In a placental mammal, the placenta is the structure that allows the developing fetus to

(A) produce its own gametes for future reproduction
(B) exchange nutrients, oxygen, and wastes with the mother ✓
(C) carry out photosynthesis to obtain energy
(D) mix its blood directly with the blood of the mother

Worked solution

$\text{O}_2,\ \text{nutrients} \rightarrow \text{fetus}$ Materials diffuse from mother to fetus.

$\text{CO}_2,\ \text{wastes} \rightarrow \text{mother}$ Wastes diffuse from fetus to mother across the placenta.

Answer: exchange nutrients, oxygen, and wastes with the mother

The placenta is the organ where dissolved materials such as oxygen, nutrients, and wastes are exchanged between mother and fetus while the two bloodstreams remain separate.

Question 87 · 2 pts

After fertilization, a single-celled zygote develops into a multicellular embryo. The process that is mainly responsible for increasing the number of cells during this development is

(A) fertilization
(B) digestion
(C) mitotic cell division ✓
(D) meiotic cell division

Worked solution

$\text{zygote} \xrightarrow{\text{mitosis}} \text{many identical cells}$ Repeated mitotic divisions increase cell number.

$\Rightarrow \text{differentiation} \Rightarrow \text{embryo}$ Cells then specialize into tissues.

Answer: mitotic cell division

A zygote grows into an embryo through repeated mitotic divisions that produce genetically identical cells, which then differentiate into specialized tissues.

Question 89 · 2 pts

In a pregnant human, the placenta and umbilical cord connect the developing fetus to the mother. Which statement best describes how the fetus obtains oxygen and nutrients such as glucose?

(A) The mother's blood flows directly into the fetal blood vessels, mixing the two blood supplies.
(B) Oxygen and glucose diffuse across the placenta from the mother's blood to the separate fetal blood supply. ✓
(C) The fetus makes its own oxygen and glucose by carrying out photosynthesis in its cells.
(D) Nutrients reach the fetus only through the muscular wall of the uterus, not through the placenta.

Worked solution

$\text{maternal blood} \ne \text{fetal blood (kept separate by the placenta)}$ The two blood supplies do not mix.

$O_2,\ \text{glucose} \xrightarrow{\text{diffusion}} \text{fetus}$ Materials cross the placenta by diffusion down their concentration gradients.

Answer: Oxygen and glucose diffuse across the placenta from the mother's blood to the separate fetal blood supply.

The placenta allows exchange of materials by diffusion between the mother's blood and the fetus's blood, which remain separate; the two blood supplies never mix.

Question 91 · 2 pts

In a certain animal, each body (somatic) cell contains $36$ chromosomes. How many chromosomes would normally be present in one of this animal's egg cells and in a zygote formed by fertilization?

(A) Egg cell = 36 chromosomes; zygote = 72 chromosomes.
(B) Egg cell = 18 chromosomes; zygote = 36 chromosomes. ✓
(C) Egg cell = 18 chromosomes; zygote = 18 chromosomes.
(D) Egg cell = 72 chromosomes; zygote = 36 chromosomes.

Worked solution

$\text{egg (gamete) number} = \frac{36}{2} = 18$ Meiosis halves the chromosome number when forming an egg.

$18\ (\text{egg}) + 18\ (\text{sperm}) = 36$ Fertilization joins two gametes and restores the full diploid number in the zygote.

Answer: Egg cell = 18 chromosomes; zygote = 36 chromosomes.

Gametes are produced by meiosis and carry half the chromosome number; fertilization of an egg by a sperm restores the full number in the zygote.

Question 92 · 2 pts

During the human menstrual cycle, the lining of the uterus thickens in preparation for a possible pregnancy. This thickening and its maintenance are primarily controlled by

(A) digestive enzymes released by the pancreas.
(B) antibodies produced by white blood cells.
(C) hormones such as estrogen and progesterone secreted by the ovary. ✓
(D) neurotransmitters released by motor neurons at muscles.

Worked solution

$\text{ovary} \rightarrow \text{estrogen, progesterone}$ Reproductive cycles are regulated by hormones, which are chemical messengers.

$\text{hormones} \rightarrow \text{uterine lining thickens and is maintained}$ These ovarian hormones prepare and maintain the uterine lining for a possible pregnancy.

Answer: hormones such as estrogen and progesterone secreted by the ovary.

Reproductive events like the menstrual cycle are controlled by hormones; estrogen and progesterone from the ovary cause the uterine lining to thicken and be maintained.

Question 93 · 2 pts

A strawberry plant reproduces asexually by sending out runners that grow into new plants. Compared with strawberry plants produced by sexual reproduction, the offspring produced by the runners are

(A) genetically identical to the parent plant, so this group shows little genetic variation. ✓
(B) formed by the fusion of two gametes from the same plant.
(C) genetically different from the parent because each runner combines two different sets of genes.
(D) always better adapted to a changing environment than sexually produced offspring.

Worked solution

$\text{1 parent} \xrightarrow{\text{mitosis}} \text{offspring on runner}$ Asexual reproduction uses one parent and mitosis, with no gametes.

$\text{offspring DNA} = \text{parent DNA} \Rightarrow \text{low variation}$ Genetically identical offspring mean little variation, a disadvantage if conditions change.

Answer: genetically identical to the parent plant, so this group shows little genetic variation.

Asexual reproduction uses one parent and mitosis, producing offspring genetically identical to the parent; the resulting lack of variation can be harmful if the environment changes.

Question 12 · 2 pts

In humans, a sperm cell containing 23 chromosomes fuses with an egg cell containing 23 chromosomes during fertilization. Which statement correctly describes the resulting zygote?

(A) It contains only the chromosomes from the egg cell, since the sperm only provides genetic instructions without chromosomes
(B) It contains 92 chromosomes because chromosome number doubles at fertilization
(C) It contains 46 chromosomes, restoring the normal diploid chromosome number for the species ✓
(D) It contains 23 chromosomes, the same number as each gamete

Worked solution

$Gametes are haploid, each containing half the normal chromosome number (23 in humans) as a result of meiosis.$ haploid gametes

$Fertilization combines the chromosomes from the sperm (23) and the egg (23).$

$23 + 23 = 46 chromosomes in the resulting diploid zygote, matching the normal chromosome number for human body cells.$

Answer: It contains 46 chromosomes, restoring the normal diploid chromosome number for the species

Fertilization restores the diploid chromosome number by combining the haploid chromosome sets of the sperm and egg, so a human zygote normally has 46 chromosomes, the same number found in other body cells.

Question 86 · 2 pts

Sexual reproduction usually produces greater genetic variation among offspring than asexual reproduction does. The best explanation for this difference is that sexual reproduction

(A) makes each offspring an exact genetic copy of one parent
(B) causes a much higher rate of mutation in the DNA of offspring
(C) gives each offspring twice the chromosome number of each parent
(D) produces new combinations of genes by combining genetic material from two parents ✓

Worked solution

$\text{meiosis} \Rightarrow \text{chromosomes sorted into gametes}$ Different gametes carry different gene combinations.

$\text{random fertilization} \Rightarrow \text{many possible offspring}$ Two parents' genes combine in new ways.

Answer: new gene combinations from two parents

Meiosis sorts chromosomes into gametes in many different ways and fertilization randomly unites two gametes, so offspring inherit new combinations of genes from both parents.

Question 88 · 2 pts

Researchers removed the nucleus from a body cell of an adult frog and inserted it into a frog egg cell whose own nucleus had been removed. The egg developed into a tadpole. This tadpole is best described as

(A) a clone, genetically identical to the frog that donated the body-cell nucleus ✓
(B) genetically identical to the frog that donated the egg cell
(C) a product of meiosis carrying half the normal chromosome number
(D) a new combination of genes from two different parent frogs

Worked solution

$\text{donor nucleus (full DNA)} \rightarrow \text{enucleated egg}$ All genetic information comes from one body cell.

$\text{development by mitosis} \Rightarrow \text{DNA} = \text{donor DNA}$ Mitosis copies the donor genome into every cell.

Answer: a clone of the nucleus donor

Because all genetic information came from the single donor body-cell nucleus and development proceeded by mitosis, the new organism is a clone genetically identical to the nucleus donor.

Question 90 · 2 pts

A skeletal muscle cell and a pancreas cell taken from the same person contain identical DNA, yet they have very different structures and functions. Which statement best explains this difference?

(A) Random mutations during development changed the DNA sequence differently in each cell type.
(B) Different genes are expressed (turned on) in each cell type as the cells differentiate. ✓
(C) Meiosis removed certain chromosomes from the pancreas cell, leaving it with fewer genes.
(D) The muscle cell and the pancreas cell contain completely different genes because they do different jobs.

Worked solution

$\text{muscle cell DNA} = \text{pancreas cell DNA}$ All body cells of an organism are produced by mitosis and carry identical DNA.

$\text{different genes ON} \Rightarrow \text{different proteins} \Rightarrow \text{different cell types}$ Differentiation results from different genes being active (expressed) in different cells.

Answer: Different genes are expressed (turned on) in each cell type as the cells differentiate.

Every body cell of an organism contains the same genetic information; specialization (differentiation) happens because different genes are switched on in different cell types.

Question 95 · 2 pts

In a cloning experiment, the nucleus is removed from an unfertilized egg cell of frog A and replaced with the nucleus from a body cell of frog B. The egg is then stimulated to develop. The resulting tadpole will be genetically

(A) different from both frogs, since the new combination creates a unique organism.
(B) identical to frog A, because the egg's cytoplasm came from frog A.
(C) a blend, with half its genes from frog A and half from frog B.
(D) identical to frog B, the source of the transplanted nucleus. ✓

Worked solution

$\text{egg A nucleus removed} \Rightarrow \text{no nuclear genes from frog A}$ The genetic information (DNA) of a cell is in its nucleus.

$\text{frog B nucleus inserted} \Rightarrow \text{offspring DNA} = \text{frog B}$ No fertilization or meiosis occurs, so there is no recombination; the clone matches the nucleus donor.

Answer: identical to frog B, the source of the transplanted nucleus.

An organism's nuclear DNA determines its genetic makeup; since frog B's nucleus was transplanted and no fertilization occurred, the offspring is a genetic clone of frog B.

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