The official name of the country is changed from Ceylon to Sri Lanka and Buddhism is made the official state religion. The Tamil parties refused to participate in the framing of the Constitution, claiming that it did not contain any minority rights protection clause that the earlier Soulbury Constitution included under its Section 29.

Sources
Constitutional Reforms since Independence, Official website of the Government of Sri Lanka; A. Jeyaratnam Wilson (1988): The Break-up of Sri Lanka: The Sinhalese-Tamil Conflict, Marianne Heiberg (2007): Terror, Insurgency, and the State: Ending Protracted Conflicts.

Extracts from the Constitution
“The Constitution of the Republic of Sri Lanka (Ceylon) adopted and enacted by the Constituent Assembly of the People of Sri Lanka on the 22nd of May 1972. …

CHAPTER I – THE PEOPLE, THE STATE AND SOVEREIGNTY …

2. The Republic of Sri Lanka is a Unitary State.
3. In the Republic of Sri Lanka, Sovereignty is in the People and is inalienable.
4. The Sovereignty of the People is exercised through a National State Assembly of elected representatives of the People. …

CHAPTER II – BUDDHISM
6. The Republic of Sri Lanka shall give to Buddhism the foremost place and accordingly it shall be the duty of the State to protect and foster Buddhism while assuring to all religions the rights granted by section 18 (1) (d).

CHAPTER III – LANGUAGE
Official Language
7. The Official Language of Sri Lanka shall be Sinhala as provided by the Official Language Act, No. 33 of 1956.
8. (1) The use of the Tamil language shall be in accordance with the Tamil Language (Special Provisions) Act. No. 23 of 1958. …

CHAPTER VI – FUNDAMENTAL RIGHTS AND FREEDOMS
18. (1) In the Republic of Sri Lanka
(a) all persons are equal before the and are entitled to equal protection of the law;
(b) no person shall be deprived of life, liberty or security of person except in accordance with the law;
(c) no citizen shall be arrested, held in custody, imprisoned or detained except in accordance with the law;
(d) every citizen shall have the right to freedom of thought, conscience and religion. This right shall include the freedom to have or to adopt a religion or belief of his choice, and the freedom, either individually or in community with others and in public or private, to manifest his religion or belief in worship, observance, practice and teaching;
(e) every citizen has the right by himself or in association with others, to enjoy and promote his own culture;
(f) all citizens have the right to freedom of peaceful assembly and of association;
(g) every citizen shall have the right to freedom of speech and expression, including publication;
(h) no citizen otherwise qualified for appointment in the central government, local government, public corporation services and the like, shall be discriminated against in respect of any such appointment on the ground of race, religion, caste or sex;

Provided that in the interests of such services, specified posts or classes of posts may be reserved for members of either sex:
(1) every citizen shall have the right to freedom of movement and of choosing his residence within Sri Lanka.
(2) The exercise and operation of the fundamental rights and freedoms provided in this Chapter shall be subject to such restrictions as the law prescribes in the interests of national unity and integrity, national security, national economy, public safety, public order, the protection of public health or morals or the protection of the rights and freedoms of others or giving effect to the Principles of State Policy set out in section 16.

Opinion
“The coup de grace came when the Sri Lanka Freedom Party and its Marxist allies in the United Front of 1970 pledged at the general elections in that year to remove section 29 (2) and replace the 1947-72 Constitution if elected to power. This was accordingly implemented when the Republican Constitution of 1972 was adopted. … In the name of this blanket provision [Section 18 (2)] the state could, without difficulty violate the rights of ethnic minorities; to violate the rights of ethnic Buddhist majority would be difficult because the governments’ dependence for their sustenance on the Sinhalese Buddhist electors”. Source: The Break-up of Sri Lanka: The Sinhalese-Tamil Conflict, A. Jeyaratnam Wilson, 1988.

“Among the most contentious provisions, from a Tamil perspective, Buddhism was given the “foremost place” among the religions and the states entrusted to protect and foster Buddhism. Sinhala was made the official language, this in one interpretation, enshrining the 1956 Sinhala Only Act, as an inviolable and nonnegotiable constitutional principle. And Section 29 of the Soulbury constitution was deleted and not replaced by explicit judicial protections for minorities. Last, the 1972 constitution subjugated the judiciary to the control of the legislature by eliminating appeals to the British Privy Council on constitutional issues. This measure was a response to a Supreme Court finding against the 1956 Sinhala Only Act …” Terror, Insurgency, and the State: Ending Protracted Conflicts, Marianne Heiberg, 2007.

Related events
September 1944
1947
November 1948
4 February 1978